In School Variation

According to Sutton Trust Report 'Improving the impact of teachers on pupil achievement in the UK':

The biggest single variable that explain variation in achievement is teachers; it is estimated to have an impact of up to 30%.

Pupils can gain up to 1.5 years' worth of learning with very effective teachers.

Report concludes that "The leadership of subject or phase teaching has to start and end with the issue of consistency and variation."