One of the best mathematics lessons I ever taught was on ratios and fractions. It involved setting up three tables at the front of the classroom. On one, I placed a single bag of Maltesers; on the second, two bags; and on the third, three bags.
When the students arrived I told them that they could share the Maltesers among themselves. There was, of course, a catch. They had to line up behind one of the three tables, and the lines behind each would have access only to the bags on that table. Hence they had to work out how many students should go behind each table to maximise their reward.
Before students could join a queue, they had to justify their choice to me with a fraction or ratio. Once they had made their decision, I gave them the chance to persuade the undecided to join rival tables, again having to back up their arguments with a fraction or ratio.
I sat back and watched as they justified their reasons for joining certain tables, and as they tried to estimate how many students should go to one table and not another. The conversation between students was exciting and mathematically rich as they tried to vindicate their arguments, and I believe that the success of this activity was down to the vested interest the class had in the chocolatey outcome.
I tried the activity again a few days later with a different class and this time used bars of Cadbury chocolate. I found these worked even better - the students could carry out more calculations because they knew exactly how many blocks made up a full bar and how best to share it out.
Yet it is the first lesson I remember most fondly, with its excitement and novelty. It really was a fantastic way to engage the children in mathematics, and in its adapted form I have used it many times since.
Gareth Fairclough teaches mathematics at Thornleigh Salesian College in Bolton, Greater Manchester (you can find him on Twitter as @gareth1512).