Gender Expectations and Stereotype Threat - a study carried out by academics from the University of Kent - found that boys also believe this by the time they reach the age of eight, the Guardian reports.
In addition, it was argued that teachers have lower expectations of male pupils.
Children were shown pictures and asked to decide who was cleverer and better behaved.
Researcher Bonny Hartley commented: "By seven or eight years old, children of both genders believe that boys are less focused, able and successful than girls – and think that adults endorse this stereotype… There are signs that these expectations have the potential to become self-fulfilling in influencing children's actual conduct and achievement."
The study said teaching staff should be discouraged from using terms such as "silly boys" and "schoolboy pranks".
Female pupils outperformed their male counterparts in the majority of GCSE and A-level subjects once again this year.