This paper examines the impact of the Programme for International Student Assessment (PISA) on education systems in Europe, particularly in Finland, Germany, and the United Kingdom. PISA, a major component of the OECD's educational work, measures the comparative performance of educational systems through tests commissioned by the OECD. The paper discusses the OECD's role in establishing the 'comparative' turn and describes PISA's management and effects. It highlights how PISA has become an influential tool for governing European education, shaping national and transnational policies. The paper concludes that PISA, through its direct impact on national education systems, has become an indirect but influential tool for governing the European education space by numbers. It also explores how key European policy actors view PISA and its effects, emphasizing its significance in building a competitive and cohesive European education space.This paper examines the impact of the Programme for International Student Assessment (PISA) on education systems in Europe, particularly in Finland, Germany, and the United Kingdom. PISA, a major component of the OECD's educational work, measures the comparative performance of educational systems through tests commissioned by the OECD. The paper discusses the OECD's role in establishing the 'comparative' turn and describes PISA's management and effects. It highlights how PISA has become an influential tool for governing European education, shaping national and transnational policies. The paper concludes that PISA, through its direct impact on national education systems, has become an indirect but influential tool for governing the European education space by numbers. It also explores how key European policy actors view PISA and its effects, emphasizing its significance in building a competitive and cohesive European education space.