Hartley & Sutton studied 140 children in three primary schools in Kent; they were split into two groups. In one group, the teacher and the children were told that boys do not perform as well as girls. The other group were not told anything. The two groups were tested in maths, reading and writing before the experiment and later on. In the group who had been told that boys do worse, the boys performed significantly worse in the tests than the girls, whereas in the control group the performance was similar.