Research from the Education Policy Institute and The Prince’s Trust said wellbeing and self-esteem were similar in all children of primary school age.
Boys and girls’ wellbeing is affected at the age of 14, but girls’ mental health drops more after that, it found.
A lack of exercise is another contributing factor – exacerbated by the pandemic, the study said.
According to the research:
One in three girls was unhappy with their personal appearance by the age of 14, compared with one in seven at the end of primary school
The number of young people with probable mental illness has risen to one in six, up from one in nine in 2017
Boys in the bottom set at primary school had lower self-esteem at 14 than their peers
The wellbeing of both genders fell during adolescence, with girls experiencing a greater decline, the report said.