According to this article in the Telegraph, Parents who want to secure a home close to the country's top performing state secondary schools face additional costs of up to £636,132 (avg. boost to houses near Beaconsfield High School).
Of course, the amount by which house prices are boosted depends on the area, how good the school is, and the relative scarcity of good schools (or affordable private schools) in the area.
Another reason to lobby for investment in our state education system!
In 2015, house prices in the postal districts of the top 30 state schools in England – defined as those secondary schools that achieved the best GCSE results in 2014 – were on average £40,728 higher than in neighbouring locations.