Girls who lack confidence in their sporting skills will avoid taking part in activities with boys, the conference was told.
Two studies looking at 70 girls and 10 boys found that young people are most likely to want to participate in sports when they see someone of their own sex involved. Dr Della Fazey, of the University of Wales, Bangor, told delegates: "Mixed-sex PE lessons should be avoided for girls with low competence."
During the studies, teenagers were shown pictures of boys and girls playing different sports and asked whether they would be keen to participate.
Researchers found that while high-ability girls were happy to take part in sports with the opposite sex, their lower-ability classmates were less keen.
Low-ability girls were also less keen to participate in sports, such as rugby and football, which are commonly seen to be for males.
"Stereotypes appear to create more of a barrier to participation for those whose perceptions of competence are not high than they are to those who feel more confident," Dr Fazey said.
Boys said they were happy to take part in sports such as netball as long as they were playing with other boys.
Research presented to the conference by Nicola Ridgers, from John Moores university, Liverpool, showed girls fear criticism in PE lessons more than boys do, a difference which gets wider as pupils get older. She said PE teachers should encourage teenagers to focus on skill development, rather than on competing against other pupils.
Boys and girls' willingness to participate in sex-stereotyped sports by Della Fazey, Ailbhe Healy and Anne-Marrie Corner is available from firstname.lastname@example.orgPerceptions of athletic competence and fear of negative evaluation during physical education by Nicola Ridgers, Della Fazey and Stuart Fairclough is available from email@example.com