Building a trustworthy knowledge base for mathematics teacher education–the mission of Mathematics Teacher Educator–requires that manuscripts convey more than stories of practice, however compelling. Manuscripts must include evidence of the effectiveness of the intervention being described beyond anecdotal claims or personal intuitions. As the Editorial Panel articulated in the call for manuscripts, “the nature of evidence in a practitioner journal is different from that in a research journal, but evidence is still critically important to ensuring the scholarly nature of the journal. Thus, authors must go beyond simply describing innovations to providing evidence of their effectiveness. Note that effectiveness implies that something is better and not just different as a result of the innovation.” Hence, claims must be supported by evidence. In this editorial, I discuss the nature of evidence appropriate for articles in Mathematics Teacher Educator