This morning, I think I taught one of my best lessons. I’ve been trying to hold off the blogging recently for the AfL Symposium but I thought people might be interested. And besides, Mark Enser has been nagging people to write about this for ages so why not give it a crack?

Quantitative Chemistry (QC) isn’t exactly a standard contender for a “best lesson.” It’s abstract and confusing and normally students just retain various bits and pieces from the three or four different methods they learn and apply them in haphazard ways. It’s probably the hardest topic in the GCSE course.

This morning, I made all that clear to my Year 11 doubles. It’s a group with a very broad range of abilities and I told them it would be hard. I told them I would be teaching them using a method called Direct Instruction, where I was going to break down the topic into the smallest chunks imaginable and have them practise each chunk before moving on. I told them that they would know they were succeeding if they were finding it easy and – dare I say – boring.

So that’s how we did it. Previously, I had broken the topic up and built SLOP (Shed Loads of Practice) booklets for the students to do. No powerpoints, no crazy activities. Me, with a board pen. Explain, practise, review. Rinse and repeat.

Below is a list of the “craft” type stuff that I tried throughout the lesson (it was a double).

  1. Spend more time on explanations: I did all explanations at least twice
  2. Used concrete examples
  3. Lots of worked examples
  4. Introduced one thing at a time – did not have them use any other chemistry other than what they were focussing on right then (If you are a science teacher, I’ve written the exact steps in an appendix at the bottom)
  5. Based on when I used the booklet with another class gave them the answers to select questions and made them do the working to get there (the booklets were already printed so no time to change hard copies)
  6. Anticipated specific errors based on another class’s work
  7. Had students do all their marking in red pen. I know this sounds trite, but it meant I could quickly breeze around the classroom while they were working, glance at their pages and see how many they were getting right and how many wrong.
  8. Intervened quickly with struggling students. I had made them follow a very specific format to write their answers (thanks Doug) and could quickly identify error. If they hadn’t followed the format I refused to help them until they redid it.
  9. Had extension work ready in the back of the booklet in the form of “interleaved questions” – random questions from all across the course

Did it work? Well, I’ll only really know in the long term, but below are some observations that indicate to me that the lesson was effective:

  • Students worked solidly for two straight hours. This isn’t always an easy class so this is a good sign.
  • Student verbal responses were very encouraging
  • Student written work and corrections (almost all students got almost every question right)
  • Students saying this is easy
  • Students saying “I’ve got this section can I skip ahead” (no)

Perhaps the most important moment though was when I was tying together mass, Mr and Avogadro’s number and showed that Avogadro’s number of atoms or molecules had a mass in grams equivalent to its Mr. A really good number of the students clearly had that “light bulb” ahhhhhhhhhhhhh moment and said “that makes so much sense!”

For a chemistry teacher, that’s the best thing ever and something I’ve never achieved before. For chemists, the world makes perfect sense. Everything is explicable and everything makes sense. It’s obvious to us what the numbers mean, which ones to use and which procedures to follow. But it isn’t to our students. And it’s why their answers are usually such a tangled mess of confused procedures, steps out of order and concepts incorrectly applied. Sure, when I see them after half term they will probably have forgotten everything. But right then and there, they got it. They really got it.


Appendix: the exact steps

Start with relative formula mass. Dead straightforward, explain, worked examples, student practice.

Next step is using words like “dozen,” “baker’s dozen” and “score” to run calculations. How many eggs in three dozen? How many eggs in 8.2 gross? The idea is to get them used to the idea that you can use a word to substitute for a number.

After that practice, explain that each of those words is useful to someone. It’s useful for supermarkets to talk about a dozen eggs because that’s how many they sell. It’s useful for a farm to talk about a gross of eggs, because that’s how many they sell. It is useful for chemists to use Avogadro’s number because it is a way of turning the enormous scales of atomic quantities into something tangible. Students practise using Avogadro’s number in exactly the same way they used a dozen or a score.

Next, is moles and Mr. I draw an old school scales on the board and draw a carbon atom in one cup and a hydrogen atom in the other. I ask which one weighs more and discuss how the same number on each side does not equate to the same mass. I then write on top of each atom 6.022E23 and say now I have one mole here and one mole there. Which one weighs more? Still Carbon, good. I then drop the BOMBSHELL that one mole of carbon atoms weighs 12g, which is the number we have been using from the periodic table.

Reiterate that the number we pick has to be more useful than just the number. The reason why chemists picked 6.022E23 is because it gives you the mass that you can just read off the periodic table. *Drops mic and walks off*

Show students the moles = mass/Mr equation and have them practice. Don’t bother rearranging it for them just have the rearranged form in the booklet and then questions which test that form.

Recap and go over responses.

Move on to ratios. Make sure they follow my method to the letter, even with simple examples (it’s in the booklet). Practise ratios with reference to how many youth leaders you need for a given number of youth (on a camp) and vice versa.

Time up – end of lesson!