I want to open my conclusion by thanking those who have given me valuable feedback and further reading over the last couple of weeks. I never meant to imply that these blogs were somehow the last word, or that my mind was not open to changing, so I have found the additional debate highly rewarding.

There is always more to read and I have tried to look at a good amount of the literature which has been suggested to me. However, I have not yet read anything which has changed my basic opinions. Much of the reading I have seen confirms my earlier opinions, however, as discussed, I have found the lack of a conceptual cognitive model to make predictive and causative claims to be frustrating.
All I have done here is apply foundational principles of cognitive science and evolutionary psychology to science practicals. I have not yet seen anyone else do that so I hope that I have managed to add something small to the debate.
So, are we wasting our time?
The answer was obviously never going to be as black and white as a simple yes or no. It obviously depends on the way the practical is designed and its place in a scheme of work. As Helen Rogerson has written: “So should we bin practicals? No. We should get better at them.”
Below I have tried to summarise things into a few basic pointers for consideration. My next piece will discuss how I’m planning on running my year 12 chemistry “assessed practicals” this year.
Does my objective for the practical respect my students’ working memory (WM)?
If I have planned a practical whereby they use their results to discover some principle, then I have not respected my students’ WM.
Whatever my objective for the practical, if my students only have minimal pre-existing knowledge of the area then I have not respected my students’ WM.
If I am expecting them to complete the practical procedure and have a simultaneous  “minds-on” approach whereby they are thinking about the scientific meaning of the practical, I have probably not respected my students’ WM. My students are novices, not experts. As long as they remain novices they will focus on the surface details of the task (i.e. the procedure) at the expense of its deep structure (i.e. the relevant science).
On a technical lesson-design level are my instructions clear, unambiguous and easily followed in a step by step fashion? If not, then I have not respected my students’ WM.
Am I expecting my students to fully plan their practical and identify variables by themselves in a “student-led” fashion? If so, the I am not respecting their WM. I need to add more scaffolding.
If my practical is to foster generic skills like evaluation, planning or analysis, then I have not respected how much WM relies on domain specific knowledge in order to evaluate, plan or analyse.
Once WM as been adequately respected, I can start thinking about the objectives of the pracitcal. For me, the below would be a good place to start:
1) Practical to overturn a misconception/folk understanding 
In my opinion the most efficient and effective way to do this is through a demonstration. You can control the discussion, remove the WM distractors of following an instruction sheet, and apply solid principles of instruction like asking probing questions throughout. See here for an interesting checklist about when to do a demo.
2) Practical to reinforce understanding of a scientific concept
As above, this could be a demo. However you could also use this after material has been studied for students to reinforce their understanding. Out of concern for students’ WM you could make this “brains-on” in one of three ways:
A) Provide questions to probe understanding within the instructions. So after the instruction: “slide the variable resistor to the right to increase resistance” you could have “define resistance” and “what effect will increasing the resistance have on the current?” or the like.
B) Forget “brains-on” during the practical and do that stuff later. So for example you could (check your school’s policy and) take pictures of the kids at various points in the practical. Beam it onto the board and then after the practical or in a subsequent lesson discuss those points. I’m sure there are lots of other ways to do this too.
C) Further reduce the cognitive load by not only practising the knowledge required to understand the practical but also by practising the techniques to be used during the practical in advance (see also point 3 below).
The article at this link from Jonathan Osborne has a similar conclusion about the necessity to do practicals after relevant content has been learned (though he arrives there by a different method – he has no mention of cognitive science or WM). See also here for another interesting take.
I know of no studies that look at the impacts of different ways of teaching like the above on student outcomes (an RCT would be ideal). Having tried each, my experience is that B and C were most effective (but that is obviously subjective anecdotal evidence) (1).
3) Practical for students to learn a particular lab technique or “competency”
Make sure you have fully demonstrated how to use the equipment and its safe handling. You can supplement this with videos. You can also dedicate time to students engage in purposeful or deliberate practice (e.g. give students 20 minutes to practise filling a volumetric flask properly with just water before making up your standard solution).
Sharing Objectives
A lot of the literature I have seen assumes that sharing objectives with students is necessary. I’m not convinced that this is necessary but there is some interesting research about prompting students when dealing with issues of transfer (2). What this means is that if you are attempting to have students apply their knowledge in a new way, i.e. by performing a practical (or, to use Abrahams’ language: to focus on the relationship between the domain of ideas and the domain of observables), then if you prompt them with an explanation of that they will have to apply their knowledge in this way you can achieve better outcomes.
 
Conclusion
No doubt, every teacher, school and class are going to be different. The above is not a one-size-fits-all rubric. Sometimes it will fit, sometimes it won’t. I’ve found that the questions raised above have helped me in my practice, though no doubt I still have some way to go.
I suppose all this boils down to:
  1. Have you respected your students’ working memory?
  2. With that in mind, what is your objective from the practical?
  3. How are you going to share that objective and promote thought about that objective before, throughout and after the practical?
In my next post I will write about a specific example of my plan for Year 12 practicals this year.

(1) NB that I have deliberately chosen not to write about the what-it-is-like type of knowledge that I discussed earlier. I think it is a bit too ephemeral to form part of day-to-day planning.
(2) See Didau and Rose, What Every Teacher Needs to Know About Psychology, Chapter 6
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