Girls as young as four think they are cleverer, try harder and are better behaved than boys, according to new research out today.
The study, by academics at Kent University, warns that children's beliefs can become a "self-fulfilling prophecy" and influence achievement.
The researchers presented 238 children aged four to 10 with a series of scenarios such as "this child is really clever" and "this child always finishes their work" and asked the children to point to a picture of a boy or a girl to say which they thought was being talked about.
The findings show that girls said that girls were more likely to have better conduct and achievement in all areas.
By the age of seven and eight, boys also believe that their female classmates are more likely to be smarter than them.
The study advises that phrases such as "silly boys", and "schoolboy pranks" are likely to contribute to the expectation that boys behave worse and underperform compared to girls.