Some pupils are naturally brighter than others, a study of twins suggests

The research shows that inherited intelligence accounts for almost two thirds of marks in GCSEs, while the amount of work done in class accounts for the rest. This suggests that raising the standard of teaching in schools may have a limited impact on children’s academic achievement when compared with the genes they are born with. Or, put more simply, nature trumps nurture. Analysis of the GCSE results of more than 11,100 of them suggested genetic background had a substantial impact on their results. In science it accounted for 58% of scores, in math for 55% and English 52%. IQ scores have been linked with genes before and the advantage appears to increase with age. Little genetic differences become bigger and bigger as you go through life.