Although young, they can begin to understand that this method is the only way to be sure that what you changed (independent variable) is affecting what you measuredobserved (dependent variable).

While looking at the recent science Sats mark scheme I have to wonder if the Qualifications and Curriculum Authority understands this very important point. It appears that one question was misleading or ambiguous or both.

Paper A, question 5(d) was about testing the strength of thread and asked children to tick one box to suggest if variables: must be the same; must be different; make no difference. QCA thinks that the colour of the thread “makes no difference” (no mark for ticking “must be the same”). It only takes a brief internet search to discover that the dyeing process affects the tensile strength of thread, some weakening the thread by up to 7 per cent.

QCA also thinks that the person pulling the thread “makes no difference” (no mark for ticking “must be the same”). Another internet search reveals that items (in this case the thread) will part at a different load depending on how the load is applied. Is it possible that any two people can apply the same load in the same way?

I am worried that the children I teach will not receive credit for this question even though they understand the concept of fair testing more deeply than the question probes. But then again, maybe they will be the scientists of the future because of their understanding of fair testing.

Nancy Bilderbeck 83 Warrington Crescent Maida Vale London W9.