Data about processes and outcomes of preschool teacher education is scarce. This paper examines the opportunities to learn (OTL) of prospective preschool teachers (N = 1,851) at different types and stages of preschool teacher education and their relation to general pedagogical knowledge (GPK), mathematics pedagogical content knowledge (MPCK), and mathematical content knowledge (MCK) with standardized tests. Process indicators in terms of OTL and outcome indicators in terms of knowledge varied substantially across teacher education types and stages. Controlling for preschool teachers’ background, multilevel models revealed that OTL in general pedagogy and mathematics pedagogy provided during teacher education were significantly related to GPK and MPCK. Effect sizes reached up to 2 thirds of a standard deviation. OTL in mathematics pedagogy were in turn significantly related to the type of institution that offered a program in favor of pedagogical colleges compared with vocational schools. OTL were also significantly related to program stage in favor of the last year of preschool teacher education compared with the beginning. Process characteristics in terms of OTL mediated fully or partly structural characteristics of teacher education such as type of institution or program stage. These results suggest that the OTL provided are more important than whether prospective preschool teachers were at the beginning or the end of their program or whether they were prepared at vocational schools or pedagogical colleges (although entrance differences have still be taken into account). It may be an important responsibility of policymakers then to ensure that all prospective preschool teachers receive sufficient OTL. The final version of this reseach has been published in the Journal of Educational Psychology. © 2017 American Psychological Association