I support the expansion of School Streets (timed road closures around schools). My officers have been working with Public Health England, London Councils and other partners to pilot School Superzones - healthy zones in the 400m around schools. School Streets is one example of the kind of intervention that could be implemented to create healthier environments within School Superzones.
Most schools are located on borough roads and will need to work with local authorities to implement School Streets. The London Borough of Hackney has produced guidance to help other boroughs to do this https://news.hackney.gov.uk/hackney-council-launches-nationwide-blueprint-to-ban-traffic-outside-schools/ and I would encourage all boroughs to support these initiatives in their area.