The review was carried out for the Scottish Office. The authors found that, in primary schools, the strong evidence for the effect of ability grouping was in mathematics. In the secondary school, where ability groups are formed by setting or streaming, the social disadvantages of these forms of organisation made ability grouping hard to defend. Yet mixed-ability grouping has its own drawbacks. Mixed-ability classes are hard to manage and to teach.
Some studies lend support to ability grouping, others point in the opposite direction.
Many show that there is little difference that can be attributed to the type of grouping alone. This is because this is a very difficult area for research. Studies generally involve comparing classes containing a full range of ability with those in which pupils are more similar in ability. However the relative performance of pupils is affected by many factors other than the mix of ability. Other factors include class size, teaching methods and materials, the degree of differentiation, the teacher's attitude towards mixed-ability teaching, and the demands of the subject being taught.