Summary of the latest Permitted Development changes - May 30th 2013. 

Minor Operations [Part 2, Class A]

This small change allows schools to erect a fence, wall or other means of enclosure up to 2m in height adjacent to a highway - rather than the normal height limit of 1m – provided: ‘it does not create an obstruction to the view of persons using the highway as to be likely to cause danger to such persons’.

A somewhat subjective test!