This article comparatively examines expertise and policy-making related to school maturity in postwar Czechoslovakia and Poland. Through an analysis of published sources and archival material, it traces the intensive development of pedagogical and psychological expertise about school maturity from the early 1960s onward and examines how that development influenced the policies introduced in both countries in the late 1960s and early 1970s. Using the concept of the expertise as a network as our analytical lens, we show that despite considerable differences in education systems and particular features of expertise in the two countries, pedagogical expertise affected policies in a very similar way through intensive networking, leading to the introduction of measures such as preparatory departments and compensatory classes in Czechoslovakia and early enrollment in Poland. We argue that educational policy-making in post-Stalinist Czechoslovakia and Poland was largely expert-driven. Nevertheless, there were limitations on the experts’ influence, as not all the proposed changes were introduced.