It suggests apprenticeships are more likely to go to men due to labour market discrimination and the types of jobs for which such schemes are available.
Unesco's 10th Education for All Global Monitoring Report suggests a gender pay gap still exists in UK apprenticeships.
It cites research that shows female apprentices in the UK earn 21% less, on average, while training. The wage benefit for a woman completing an apprenticeship is 4%, compared with 20% for a man. It also says apprentices are more likely to be men due to "discrimination in the labour market and the types of occupations for which apprenticeships are available".
The study also reveals that in the UK, schools play a less active role in helping youngsters to secure an apprenticeship.
Around two-fifths (42%) of secondary school leavers who start apprenticeships apply directly to an employer, it says, while just 10% find them through their connections and 10% secure one through a careers adviser or teacher.
The report adds that due to the economic crisis, a lack of youth skills becomes increasingly damaging.
Unesco director-general Irina Bokova said: "These young people should not be seen as a threat.
"It is to everyone's benefit that we quickly start realising they represent an opportunity."