Today, many raise concerns about the over-representation of females in teaching. It is said that the increase in female teachers leads to a dominant teaching style with a focus on communication, literacy and cooperation. This style is assumed to favour girls. The prevalence of behaviour problems and underachievement in boys is suggested to be related to feminisation of education. This hypothesis is investigated by the analyses of data from nearly 9,000 children attending primary school. Parents and teachers evaluated the behaviour of children at 7, 10 and 12 years of age by use of questionnaires. The analysis of data took place by cohort. Boys exhibit more behaviour problems related to ADHD and externalising behaviour than girls. The difference in behaviour between boys and girls was found to be unrelated to the sex of the teacher. This outcome is consistent, the relation between sex of the teacher and behaviour problems of children is insignificant at each age and according to teachers, mothers and fathers. In contrast with popular views, the relationship between female teachers and behaviour problems in boys is too small to be detected.