Abstract: This article defends the view that markets in education need to be restricted, in light of the problem posed by what I call the ‘educational arms race’. Markets in education have a tendency to distort an important balance between education’s role as a gatekeeper – its ‘screening’ function – and its role in helping children develop as part of a preparation for adult life. This tendency is not merely a contingent fact about markets: It can be traced to ways in which education is a partly positional good and how markets respond to (and stimulate) demand for positional goods over non-positional goods. The problem with arms races is that they allow markets to facilitate wider use of defection in a collective action problem. Using these claims, I argue that markets in education have a distinctive tendency to become objectionably exploitative. I conclude by applying some of my conclusions to illuminate various egalitarian claims about justice in education.