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My best lesson - Tilt the balance to create a feeling of pride

One of my best chemistry lessons is a testament to the increasing level of understanding that younger students are gaining for sciences.

The content was originally devised for 16- to 18-year-olds, but I now feel comfortable using it for 15- to 16-year-olds - they are more than prepared to tackle the challenging material.

And it certainly is a difficult topic: Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

The lesson begins with a general explanation of equilibrium. We look at a specific reversible reaction and at how changing the concentration andor pressure of one of the reactants would affect the position of equilibrium and the quantities of specific reactants and products. We then discuss the effect of increasing or decreasing the temperature.

The students are now ready to move on to the main part of the lesson: a marketplace activity. They are divided into four groups of similar ability and given a laminated sheet with a reversible reaction written on it. Each group has a different reaction to discuss and is given three questions focused on Le Chatelier's Principle.

It may surprise other subject teachers, but students really get into this debate. They tend to carry out their discussions so intently that I could leave the room unnoticed.

After 15 minutes, four new groups are formed, consisting of members from each previous group. The laminated sheets are brought together and - here's the key - students reveal to their peers the results of their previous group's discussions. In this way, the students become the teachers.

Once every group is confident that it understands the concepts, each student undertakes to answer an exam question on what has been learned. When they have been allowed enough time to answer, the students again take charge of the lesson: they peer-assess each other's work using the mark scheme.

The results are always superb, and students feel they have learned something with little teacher input.

Lisa Severs is a science teacher at Egglescliffe School in Stockton-on-Tees, England.

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