This paper investigates the claim that the shift from a selective to a comprehensive school system had a deleterious effect on social mobility in Great Britain. Using data from the National Child Development Study, we compare the chances, for both class and income mobility, of those who attended different kinds of school. Where media attention focuses exclusively on the chances for upward mobility of those children from lowly origins who were (or would have been) judged worthy of selection into a grammar school, we offer more rounded analyses. We match respondents in a way that helps us to distinguish those inequalities in mobility chances that are due to differences between children from those due to differences between the schools they attended; we look at the effects of the school system on the mobility chances of all children, not merely those from less advantaged origins; and we compare comprehensive- and selective-system schools, not merely comprehensive and grammar schools. After matching, we find, first, that going to a grammar school rather than a comprehensive does not make low-origin children more likely to be upwardly mobile but it helps them move further if they are; second, that grammar schools do not benefit working-class children, in terms of class mobility, more than they benefit service-class children, but, in terms of income mobility, such schools benefit low-income children somewhat more than they benefit higher-income children – that benefit relating only to rather modest and limited movements within the income distribution. Finally, however, the selective system as a whole yields no mobility advantage of any kind to children from any particular origins: any assistance to low-origin children provided by grammar schools is cancelled out by the hindrance suffered by those who attended secondary moderns. Overall, our findings suggest that comprehensive schools were as good for mobility as the selective schools they replaced.