In 2010, the ASE published the Principles and Big Ideas of Science, the product of a conference involving a number of prominent figures within the academia of science education and edited by Wynne Harlen (1). Other than Millar and Abrahams’ article on effective practical work, I think it’s probably the most commonly referred to article within UK science education. I remember reading it during my PGCE, and not being particularly swayed by it. At the time, I was a little grumpy that there was only one of the Big Ideas (BIs) that was strictly chemistry, and that the omission of collision theory or the conservation of mass was a mistake.

With a resurgence of thought around curriculum, lots of people have been writing about BIs within science as a tool for shaping or framing science curriculums. As such, I’ve revisited Harlen’s BIs to try and get my head around it and see if, and how, I should be thinking about it more deeply. As I read through the document I realised that it wasn’t really just about the Big Ideas. It was about philosophy, ideology, pedagogy and curricular studies all rolled into one, so my discussion below is about all of those things. If you aren’t particularly interested in Big Ideas of science per se, do read on anyway: there’s lots of stuff in there that you may find interesting.

This is a really big area. Really big. There’s no doubt I won’t be able to do it complete justice here, but I’ve done my best and, as ever, look forward to the debate. This is certainly one for the curriculum nerds.

Frames of reference

It’s worth noting at the outset that there will be major disagreement between myself and the BIs. The first page of the BIs starts with “principles of education,” with number one as:

Throughout the years of compulsory schooling, schools should, through their
science education programmes, aim systematically to develop and sustain learners’
curiosity about the world, enjoyment of scientific activity and understanding of
how natural phenomena can be explained.

I’ve never seen a programme that systematically develops students’ curiosity, and I would be interested to see a curriculum that looks like that – I doubt it’s possible, and evaluation and measurement would be incredibly difficult. Either way, in my view, the last part of the sentence should come first. I think the purpose of a science curriculum is to systematically increase the amount of knowledge and understanding that students have of natural phenomena. A discussion for another time is where enjoyment and curiosity come in (but, broadly, once you know more stuff you find the world more interesting too), but it’s important to note that there are two very different frames of reference and understanding of purpose and aims here.

The ideological breaks continue down the principles. Principle 2 says that:

The main purpose of science education should be to enable every individual to take
an informed part in decisions, and to take appropriate actions, that affect their
own wellbeing and the wellbeing of society and the environment.

I think this is an important purpose of science education (and the authors acknowledge other ones) but would stop short of saying it is the “main purpose.” Where is the pursuit of knowledge for its own sake? Where is the best of what has been thought and said? Where are the cultural treasures that are the intellectual inheritance of every member of humanity? I think those things are important too and, as above, we have to note that there are different frames of reference.

The other principles have similar differences in ideology. Principle 5 for example requires that content should be of interest to students and relevant to their lives, which I don’t generally agree with, normally following curriculum theorist Michael Young in arguing that:

…for a curriculum to rely on the experience of pupils alone limits what they can learn to that experience….It is this structuring of knowledge independently of the experience of pupils that offers the possibility for pupils to think beyond their experience and enable them, as the sociologist Basil Bernstein put it, ‘to think the unthinkable and the not yet thought’ (Bernstein, 2000).

Continuing with problems in the principles, for some reason principle 9 mentions the importance of formative assessment. I don’t really know why it’s there: assessment is a vitally important classroom tool, but there are many classroom tools and formative assessment seems to be the only one that makes it into the list.

I think part of the purpose of this section is about emphasising differences. There are people out there who assert that all of the new developments in education have already come before and science teachers have always thought like this. The Big Ideas should show this not to be true: such an influential and prominent document with such clear differences to the contemporary zeitgeist cannot be ignored or passed off.

What do we mean by “Big”?

Before I revisited the document, I thought about how many different ways we could think about the word “Big” as it pertains to ideas. I came up with the below potential definitions and examples:

  1. Explanatory:  an idea like “collision theory” explains rates of reaction
  2. Encompassing: an idea like “energy” encompasses thermodynamics
  3. Historically important: an idea like “natural selection” has an enormous imprint on the history of science and society
  4. Politically/societally important: an idea like “climate change” is important in staving off disastrous planetary consequences

My understanding of Harlen is that the BIs are framed as an antidote to a number of problems:

  1. Students do not find science interesting or relevant
  2. They see the subject as disconnected internally (isolated strings of facts)
  3. They see the subject as disconnected from the world around it
  4. Learning science in school has elitist historical baggage and is still seen as not for everyone
  5. Abstract ideas in secondary school are not connected to concrete experiences “from which they should be built”

I think whether or not these things are still true is up for debate. If they are still true, I think whether or not BIs can solve them is certainly debatable (as we shall see). As one final “think”, I think we’ve had schools implement Big Ideas by now, and it’s incumbent on their advocates to run an evaluation and tell us whether or not these metrics have improved. To my knowledge, no such survey exists.

In terms of addressing a solution to the problems listed above, the authors argue that:

Part of the solution to these problems is to conceive the goals of science education not in terms of the knowledge of a body of facts and theories but a progression towards key ideas which together enable understanding of events and phenomena of relevance to students’ lives during and beyond their school years (my emphasis)

A bit later on, we get to what actually defines the Big Ideas:

Here we are using the term ‘idea’ to mean an abstraction that explains
observed relationships or properties. This is different from the everyday
use of the word ‘idea’ as a thought which is not necessarily based on
evidence. A ‘big’ idea in science is one that applies to a range of related
objects or phenomena, whilst what we might call smaller ideas apply to
particular observations or experiences. For instance, that worms are well
adapted to living in the soil is a small idea; a corresponding big idea is that
living things have evolved over very long periods of time to function in
certain conditions (my emphasis)

Which looks a lot like what I’ve called “explanatory” BIs above. After reading through an extensive discussion about the purposes of science education, the authors finally get to the criteria for selection of certain ideas about science:

  • have explanatory power in relation to a large number of objects, events
    and phenomena that are encountered by students in their lives during
    and after their school years
  • provide a basis for understanding issues involved in making decisions
    that affect their own and others’ health and wellbeing, the environment
    and their use of energy
  • provide enjoyment and satisfaction in being able to answer or find
    answers to the kinds of questions that people ask about themselves and
    the natural world
  • have cultural significance – for instance in affecting views of the human
    condition – reflecting achievements in the history of science, the
    inspiration from the study of nature and the impacts of human activity
    on the environment.

Other than bulletpoint 3, that looks quite a bit like my list. What I’ll do now is briefly examine a couple of their ideas in light of the stated criteria. I’m not going to dive into their “ideas about science” now, and will limit my discussions here to the “ideas of science.”

Big Idea 1: All material in the Universe is made of very small particles

This, the first of the BIs, is my terra firma. I imagine this one was selected for its explanatory power and for its importance in the history of science (2). My problem, though, is with how it actually has explanatory power. It seems to me that what the authors are proposing is a process that goes a bit like this:

  1. Gather naive ideas as a child
  2. Slowly have those ideas challenged and experience cognitive conflict due to teacher-facilitated activities and inquiries (more on this later)
  3. Learn about specific “small ideas”
  4. Start to appreciate the “big idea” that explains the “small ideas”
  5. Be able to use knowledge of the “big idea” in an unfamiliar context

My problem here is with the sequencing and commonality. Let’s take particles as a simple example. We’ll skip over steps 1 and 2 for the minute, because 1 is obvious, and 2 probably a waste of time. Let’s think about the sequencing of small ideas to build up to our particle big idea.

In Year 7, I might teach students about the atom, molecules, giant structures and chemical bonds. Throughout all of that, I might emphasise that it’s vital to recognise that all substances are made of these tiny little particles. In future years, when doing separation techniques I might talk about what happens in terms of particles when substances are dissolved and filtered. In a later year still, I might talk about rates of reaction and collision theory. All of these illustrate the big idea. They have that in common. But there are two problems:

First, the big idea might be fully understood (as well as all the other information the BIs document includes within this big idea), but the student utterly incapable of making prediction based on it. As an example, let’s take dynamic equilibrium. You can’t really understand that without understanding that all matter is made of particles. But this particular Big Idea is laughably inadequate as a tool for explaining how a reaction might reach equilibrium. There are so many other things you need to know as well before it even begins to make sense. Put another way, if I had two students, one of whom had seen this Big Idea illustrated by filtration, and one who had missed that lesson, do I really think the first one is more likely to understand or predict equilibrium? Not a chance.

Secondly, I don’t even think it’s the most interesting thing that these topics have in common. I have some really outstanding year 11 chemists at the moment. If I asked them what do rates and filtration have in common, the least interesting answer possible would be “they are both explained by conceiving of matter as made of particles.” Even if we took closer concepts like rates and equilibrium, the most interesting answers would be about the effect of changes to the system, like pressure or temperature. And sure, those effects are explained by a kinetic and particular model, but that isn’t the interesting bit. The interesting bit is what is actually happening. The fact that we just have particles isn’t exciting, it’s obvious: tacit. The way they move, collide and result in observable effects is exciting. If I spent any time at all in class trying to tell students “hey look! These both involve particles! Scientists never used to be able to understand this, because they didn’t realise matter was made of particles but thought it was about earth, wind, water and fire!” they would look at me like I was nuts. And that’s for the two topics that are probably closest in their relation. Fractional distillation also relies on a particular model, but that’s probably the least exciting commonality it has with rates, equilibrium or any other such topic in chemistry.

Big Idea 2: Objects can affect each other at a distance

Absolutely. 100%. They can. And if you don’t understand that, you can’t understand gravity, electrostatics or magnetism. But if I asked my year 7s “I have just lifted a pen, and then let go. It fell to the floor. Why?” and someone answered “because objects can affect each other at a distance” they wouldn’t be wrong, but it isn’t right either. It’s not enough. It’s more of a threshold concept: you need to get over this to understand more, but it isn’t going to actually explain anything. And if it can’t explain anything, then it fails the tests that the authors set.

Not a Big Idea: Surface area to volume ratio

I’ve made the bold claim before that surface area to volume ratio (SA:V) is the most powerful concept in the whole of school science. In opposition to what’s been mapped out above, it explains:

  • Adaptations for heat loss
  • Adaptations for travelling on sand/snow
  • Structure of cells like the root hair, alveoli or microvilli
  • Heat loss
  • Effect of SA on rates
  • Nanoparticles’ odd properties

And so on, and so forth. But it doesn’t qualify as a “Big Idea.” And I wonder why not.

Big Idea 5: The composition of the Earth and its atmosphere and the processes occurring within them shape the Earth’s surface and its climate

This is also true. And it’s important: really important. I doubt there is a more important general topic than climate change at the moment. And yes, this doesn’t explain much, but remembering the authors’ selection criteria, it could satisfy two other bulletpoints: relating to individuals’ abilities to make decisions about their life and things of general cultural importance. But I don’t know why you need a “Big Idea” per se for this. I want students to know an absolute ton of information about the climate as it changes. I need them to know this so they can make informed decisions about the future of humanity. But that means that this “big idea” is really just a heading, a title. It’s the name of the topic, but no more than that. It’s general enough to encompass smaller topics like global warming, combustion, how the emergence of life has affected the composition of the atmosphere, but it doesn’t do more than just encompass them. It doesn’t explain them, predict them or make them any more readily understood. So one can legitimately ask: do we need a Big Idea? What’s wrong with just a list of topics?

Principles of awesome

I like the list that the authors have written. Every item on the list is a scientific construct that is important, and is necessary to understand other, “smaller” ideas. But they are not even close to sufficient. To me, they just represent some really awesome things that humanity has discovered over time. Genetics, cellular theory, thermodynamics: these are all awesome. But claiming that you can reduce them to one “Big Idea” that has some kind of power all of its own doesn’t work for me.

Curriculum, pedagogy and social constructivism

It’s worth noting that throughout the document, the authors argue in favour of a social constructivist model of education, with a heavy emphasis on inquiry learning. For example:

Appreciation of how science knowledge is developed should be derived at
least in part from experience of undertaking scientific inquiries of different
kinds…participation in forms of inquiry provides the experience for students to develop understanding about science and how scientists go about their work…Implicit in all of this is that students are taking part in
activities similar to those in which scientists engage in developing

I’ve written extensively before about why this isn’t true. In short: our students are not generating new scientific knowledge: that’s what scientists do. They are learning old knowledge, and to say that because scientists use inquiry students should too is to make a category error.

The promotion of inquiry-learning does not stop there:

An inquiry-­‐based approach is widely advocated and is being implemented in many different countries across the globe. Inquiry, well executed, leads to understanding
and makes provision for regular reflection on what has been learned, so
that new ideas are seen to be developed from earlier ones…There is growing evidence that this has a positive influence on attitudes to science

And here:

Undertaking scientific inquiry gives students the enjoyment of finding out
for themselves and initiates appreciation of the nature of scientific activity,
of the power and the limitations of science.

Of course, this is 2010. And then, the orthodoxy was indeed to promote inquiry learning. We now know differently, and many are shifting their practice towards explicit teaching in light of extensive evidence (I have written a bit about this starting here). And it’s also important to note for those who deny that inquiry was ever promoted in the highest echelon, that it was. It really was. And completely uncritically (3).

Pedagogy dictating curriculum?

Later, the authors argue this:

Inquiry-­‐based teaching is demanding, both of teachers’ skill and of time for teaching and learning. Inquiry-­‐based learning can lead to greater depth in understanding but as it takes more time the corollary is that the breadth has to be reduced. Thus identifying big ideas in science is a natural, and indeed necessary, accompaniment to promoting inquiry-­‐based science education.

To me, this is highly problematic. It is essentially arguing that because we want to do inquiry, we should change what we are going to teach (4). This is all wrong in my head. We need to decide what we are going to teach before we decide how we are going to teach it. A teaching technique is only useful if it bridges the gap between the student’s brain as it is now, and what I want my student’s brain to look like in five years’ time. To me, that is self-evident (and more here).

Can you build a curriculum without Big Ideas?

I’m really proud of the science curriculum that we’ve built at my place. It’s incredibly powerful, and our students know loads of science which they can apply in other contexts. They are excited, curious, and deeply knowledgeable. But, we have not referenced a single “big idea” in our planning, explicitly or implicitly. Sure, we include things like “everything is made of particles” or that “objects can affect each other at a distance” when we are teaching, and we spend the requisite time on them. But they don’t frame the curriculum: they aren’t the end goal. The end goal is students who know an absolute ton of science and can use it to be creative, inventive and brilliant.

A further problem: specificity

If you view your students as intrepid explorers of the physical world; guided all the while by wise and facilitating science teachers, then it makes sense to leave your curriculum pretty open. You want teachers to personalise instruction to the students in front of them: their interests and personal experiences. Under a model like that, the BIs make sense because of how much they encompass. You can frame a curriculum pretty loosely around them and fulfil your curricular intent.

Obviously though, if you view school science as a specific package of knowledge that you want your students to have, the loose model starts to break down. You start to see your students not as individual exploring mavericks, but as novices progressing through a predetermined body of knowledge and understanding. Teachers must respond to their class, both in their pedagogy and what they choose as their hinterland (all the content they use to embellish and elaborate on the core material), but sensible curricular leadership appreciates that specificity – all teachers knowing exactly what to teach and when to teach it – is a powerful model that, perhaps paradoxically, liberates students to “think the unthinkable and the not yet thought.” Big Ideas might still be relevant in such a model, but they cede primacy in curricular design to careful delineation and sequencing (5).

More useful constructs

If the Big Ideas are going to get people thinking about curriculum I’m on board. But I think there are better lenses (or constructs) through which to think deeply about curriculum. I really recommend the maps and visualisations that Ruth Walker has put together on this – trust me, you won’t regret reading her blogs (6).


I wrote this blog because I’ve seen a lot of people asking about Big Ideas, with the three scientific learned bodies all using it to frame their curricular work over the last year or so (7). Here’s my advice: if someone asks you to write your curriculum around Big Ideas (Harlen’s or otherwise) follow these steps:

  1. Check that it isn’t driven by progressive/social constructivist pedagogy. If yes, challenge.
  2. If no, ask why? Are these really the most helpful constructs for framing our curriculum? Or is it just a cute idea that doesn’t really aid our thinking?



(1) There are no serving teachers on the editorial board. It looks like a couple of contributors did teach, but it is underemphasised relative to their academic achievements. That’s not to say that academics and scientists do not have a right to an opinion: they do, and their right and expertise is important. But teachers have that right too, and it seems odd for there not to be any teachers included. It’s also worth noting that part of the distinctiveness of the current focus on curriculum is the number of frontline teachers involved.

(2) Many thanks to Bill Wilkinson for pointing out that Feynman argued that: “If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.”

(3) Many thanks to Gethyn Jones for prompting me to think about this

(4) Though there are many who no longer endorse Inquiry methods, I was recently condemned for publicly criticising the December 2018 issue of the SSR for containing 7 articles about inquiry presented completely uncritically. If you are aware of all the evidence against inquiry learning and you still think it’s a good idea that is your right, of course. But it is completely disingenuous to pretend like there is no evidence against it.

(5) As a side note, it is worth noting that traditional or explicit methods to teaching are hardly easy or without effort. I challenge anyone to look at my SLOP booklets and tell me I haven’t worked for them. I just focus my efforts in other directions: instead of desperately trying to manage behaviour in a busy and moving classroom, or direct my energies towards gently coaxing students to discover correct answers for themselves, I spend time thinking about sequencing, practice and quality of explanation.

(6) I’d also recommend her blog for the Curriculum in Science symposium which provides a glossary of important vocabulary and conceptual tools by which to think about curriculum.

(7) Even if they conceive of them as “big questions”, which strikes me as the exact opposite of Harlen’s Big Ideas. BIs are not questions – they are answers.