Previous work by the authors suggested that during the 1970s and 1980s, a person’s early cognitive ability became a less important determinant of his or her eventual educational achievement. Furthermore, over the same time period, family background started to have a greater impact on a person’s achievement. Given that this coincided with the gradual demise of the British selective grammar school system, it would seem that the role of selection (ability tracking) in the school system merits further investigation. This paper explores the inter-relationship between school selection, ability and educational achievement. Our regression and matching results indicate that the most able pupils in the selective school system did do better than those of similar ability in the mixed ability school system. We do not find evidence of significant negative effects of tracking for low/middle ability students.