"When it comes to exams, class matters" showed that students benefit from being taught alongside higher-achieving peers, while "Streams of ability"
preached denying students this advantage by segregating them. Grouping by ability, whether at school or class level, benefits some of the already-advantaged at the cost of lowering the achievement of the rest. The future prosperity of the UK depends on raising the achievement of all students, and not just a privileged few.
Professor Dylan Williams
Institute of Education, University of London