Some pupils in London are being taught in classrooms where air is so polluted it breaches World Health Organisation (WHO) guidelines, a study has found.
In some cases, the report found that pollution levels inside the schools were higher than outside.
The findings come as 50 schools in London are set to benefit from a share of £1m from City Hall to protect children from pollution.
Sadiq Khan wants the funds to allow schools to make "immediate changes".
A review of existing studies concluded that "children living or attending schools near high traffic density roads were exposed to higher levels of motor vehicle exhaust gases, and had higher incidence and prevalence of childhood asthma and wheeze".