Five years after California reduced class sizes in the equivalent of its first schools, a study of the impact of the policy in Los Angeles - one of the largest and most socially diverse school districts in the country - shows that it has been a resounding success.

Nearly 20,000 third-grade pupils (aged eight to nine) who were taught in classes of 20 achieved higher marks in standardised tests in reading, mathematics and language than the control group who were taught in classes of 30 before the new legislation was implemented.

The most striking effects of class size reductions were in schools identified as high-need, low-achieving, and with large Hispanic populations. In addition, the bnefits were 50 per cent higher for teachers who had six or more years’ experience. The researchers deduce that experienced teachers are more able to take advantage of the benefits to be gained from smaller classes.

While the report takes pains to point out that it is impossible to attribute the improved test results to class size reduction alone, since other school reforms took place at the same time, it also says that the documented improvements greatly underestimate the positive effects of smaller classes on children’s achievement.

Class Size Reduction and Third Grade School Achievement: Some Highly Encouraging Findings in the Los Angeles Unified School District by Harold Urman, Dennis Hocevar, Gwen Uman, Ted Bartell, Pat Yee and Beverley Maxwell. Correspondence to: urman@vitalresearch.com or hocevar@usc.com