We evaluate the effect on test scores of a UK education reform which has increased
funding of schools and encouraged their specialisation in particular subject areas, enhancing pupil choice and competition between schools. Using several data sets, we apply cross-sectional and difference-in-differences matching models, to confront issues of the choice of an appropriate control group and different forms of selection bias. We demonstrate a statistically significant causal effect of the specialist schools policy on test score outcomes. The duration of specialisation matters, and we consistently find that the longer a school has been specialist the larger is the impact on test scores. We finally disentangle the funding effect from a specialisation effect, and the latter occurs yielding relatively large improvements in test scores in particular subjects.