Exploring opportunities to learn (OTL) has shown great potential in recent years to better understand how pre-service teachers are prepared towards becoming competent teachers. Drawing on the framework of the Teacher Education and Development Study in Mathematics (TEDS-M) and modern validity theory, in this article, we explore inferences from OTL questionnaires across two different response formats. In a multi-cohort study conducted at a large German university, pre-service mathematics teachers provided self-reports on OTL from their respective study programs in a binary response format in the first cohort (n = 187/190), and on five-point Likert scales in the second (n = 186/250). We apply Item Response Theory (IRT) to estimate item difficulties and analyze the relation of pre-service teachers’ OTL and their Mathematical Pedagogical Content Knowledge (MPCK) as well as their General Pedagogical Knowledge (GPK). However, our results show only marginal differences between response formats. We discuss the implications of our findings in regard to modern validity theory.