The use of stereotypical expressions like "silly boys" and schoolboy pranks" by teachers, a study warns, may be fuelling the gender gap in education.
The study revealed teachers were warned against employing stereotypical language or separating classes into "boys v girls" to avoid adding to children's preconceived ideas about the gender divide.
The study, released at the British Educational Research Association annual conference at Warwick University, follows the publication of figures last week showing that boys are falling behind girls at the age of seven.
Data from the Department for Education showed that 24 percent of boys in England failed to reach the standard expected for their age group in writing compared with just 13 percent of girls.
But a report by Kent University suggests that results may be linked to girls' and boys' own perceptions of their abilities at a very young age.
Bonny Hartley, a researcher from the university's school of psychology, who led the study, said that adults could contribute to this "self-fulfilling prophecy" by dividing classes into boys v girls or using stereotypical language.
"It is widely acceptable to pitch the boys against the girls or 'harmlessly' divide the class in this way for practical ease," the Telegraph quoted her as saying.
"In addition, phrases such as 'silly boys', 'schoolboy pranks' and 'why can't you sit nicely like the girls?' are all likely to contribute to the expectation that boys behave worse and under-perform compared to girls.
"These phrases tend to slip off the tongue, yet they may be doing more harm than realised in reinforcing children's perceptions that it is acceptable to judge and evaluate people on the basis of their gender," she added.