I invented a science investigation called “Who stole the Kit-Kats?” before I came here from New Zealand. I started by taking aside a responsible, able pupil to be the “thief”. The thief left certain clues at the scene of the crime: a Kit-Kat wrapper, fingerprint, footprints and part of a note. We made a trail of footprints by drawing round his feet with chalk. Then I took the thief’s fingerprints on a transparency sheet (easy to enlarge and study), and asked the child to write on kitchen paper with a black felt-tip pen.

Next I put on my tweed cap and cape, and found a pipe. I told the class that several Kit-Kats had mysteriously disappeared, but luckily the thief had left some important clues.

I gave each child a form to fill in with a black felt-tip pen, but different groups used different brands of pen (I made sure that the thief and his group used the same brand). The name and height of each person was entered on the sheet with each pupil’s fingerprint, taken using a stamp pad. Children had to study and research the fingerprints. They measured the length of the footprint and stride and made some predictions. Was it a tall person with a long stride? Was the thief walking barefoot?

Children then had to measure their own footprints and stride and add these details to the sheet of paper.

I also got them to test the ink from their felt-tip. They took a strip of sugar paper or blotting paper, drew a line an inch from the bottom and made a blob along the line using a felt-tip pen. Then they put the strip of paper into a glass of water so that the water came up to the line. As the ink separated they could observe and note on their sheet the different colour combinations which varied from brand to brand.

Could they match the results to a particular group? I gave the thief a special award and gave a Kit-Kat to each of the rest of the class.

Melissa Christie, supply teacher, south-east London