Can selecting on the basis of academic ability at secondary school level be reconciled with equality of opportunity? One common view is that although the two can be reconciled in principle, for various contingent reasons selection tends to undermine equality of opportunity in practice, for example, it tends to advantage children who have been fortunate enough to be born into better off families. In this article, it is argued that the problems with selecting on grounds of academic ability go deeper because of the fact that children develop at different rates, and that a proper appreciation of the difficulties this creates for reconciling equality of opportunity with selection casts doubt on the meritocratic conception of equality of opportunity, including Rawls's principle of fair equality of opportunity. It concludes with some thoughts concerning what a better approach to theorising equality of opportunity would look like in light of the issues raised by secondary school selection, drawing upon social egalitarian ideas and a Dworkinian hypothetical insurance scheme.