Several types of solutions exist, from reducing the class size for groups of highly disadvantaged students, to developing special curricula, or adding additional services to existing curricula. Some students were assigned to small classes (15 students on average) in pre-school and elementary school, while others were assigned to larger classes (22 students on average). The experiment was implemented across 79 schools in Tennessee from 1985-89. An evaluation of the programme showed that assignment to a small class was associated with positive changes in personality as well as later-life earnings (Dee and West, 2008, Chetty et al. They use exogenous differences in class sizes due to rules regarding the maximum number of students in a class to identify the impact of class size. They find that one fewer child in elementary school (aged 7-8 years) increases math test score by 0.3 to 0.4 points (2.5-3% of standard deviation) and even by 0.7 points for socially disadvantaged children.