Mixed physical education classes are disliked by pupils and probably damage girls' examination results, research carried out for the Scottish Qualifications Authority has found.
Girls say boys distract, embarrass, tease and laugh at them, misbehave and lack concentration. They dominate, intimidate, are greedy with the ball, rougher and more aggressive, as well as being stronger, better competitors and hard to play against.
Boys say games are more competitive, demanding and present more of a physical challenge when girls are not around. They believe girls bring down the standard of play, do not try, want to sit out activities and forget their kit.
Researchers say boys who outperform girls in practicals are gaining unfair advantages because of the activities selected for Standard grade and Higher examinations. On average, boys record one grade more at Standard grade and one level more at Higher.
Differences are particularly noticeable in badminton, basketball and volleyball.
The SQA warns: "The psychological environment in which competitive games are played in mixed teams is frequently undermining the self-confidence of girls. This is particularly the case for girls of middle to low ability in the subject."
In the first two years of secondary, pupils and teachers back mixed activities but by third and fourth years girls and boys prefer to learn and be assessed in single-sex groups. Neither like mixed groups for swimming, creative activities and games in which strength and speed make a difference.
In fifth and sixth year, more girls support mixed groups, although many find boys patronising.
In competitive team games, teachers found it difficult to assess girls fairly, while girls could not gain experience in applying their skills in an aggressive environment, where they were often in a minority. Activities tended to reflect the interests of boys because they were in the majority.