Suppose you are mother or a father who likes to know exactly what is going on. You have been told that one set of Eleven Plus books is likely to be more useful than a different set. You gather together all of the parents of prospective eleven plus children at your school and ask them for their co-operation.
Your nephew attends a different school – but the schools are geographically very close together so the children are drawn from similar backgrounds. This then becomes the control group. These children will not be prepared for the eleven plus. (Although the school is only three miles away, the second school is in a different county so there is no eleven plus!
We need to assume that there will be no difference in the results of the children taking the examination. Half the children in the first group will use only the recommended book – while the rest of the school use a variety of eleven plus books and teaching materials.
In the first place it would be wrong to assume that using one particular eleven plus text is better than another. The hypothesis would be that there can be no difference to the test scores.
Secondly we would need to see if working on eleven plus papers actually did make a difference. We would then start with the hypothesis that there can be no difference to the scores of the two schools.
So if a mother or a father tells you that one set of books is better than another you will still need to approach this statement with some caution. What worked for one child may not work for another. The child might have been able to pass the test without having worked through a paper.