In this article, I assume that it is universally accepted that education--at least sometimes--should aim at knowledge. Moreover, I take my point of departure from the classical (and minimal) definition of "knowledge" in terms of justified true belief (JTB). I further assume that this definition usually rests on a common-sense realist notion of truth, which I take to minimally entail that "whether" something is true or not is independent of our beliefs "about" whether something is true or not, and that we--at least sometimes--can "know" whether something is true or not. Given the strong relationship between education and knowledge, these assumptions might make one think that common-sense realism has a strong position in educational research. However, it is clear that educational research has been heavily influenced by views in conflict with common-sense realism. The aim of this article is to comprehensively describe the implications of rejecting common-sense realism for the practice and aim of knowledge-based education. I outline two strategies for opponents of common-sense realism: (1) either to avoid the (realist) notion of truth altogether in the definition of knowledge or (2) to (re) define truth in the definition of knowledge in a way that avoids common-sense realism. I conclude that both strategies entail radical implications for the practice and aim of knowledge-based education. I end the article by discussing and responding to some of the concerns that have motivated scholars to reject common-sense realism in the first place.