Structure and content of teacher education depend on a deeper rationale, which is a result of cultural boundaries. At the same time teaching is a cultural practice that differs across countries. Like the water in the fish's tank, such cultural givens are too often invisible as we debate research designs. In this article, we focus in particular on the understanding of three main components of teacher education: mathematics, mathematics pedagogy and general pedagogy, and on juxtaposing two extreme models: Germany and the US. It turns out that benefits and problems of international comparisons are closely related to each other.