This article reports on Year 2 of a three-year project to assess historic site-based teacher professional development programs. The intended focus was assessing pre-post Q-sorts and interviews of 29 teachers regarding how they see their work at historic sites affecting their professional development. However, data analysis revealed exceptionally large shifts in teacher experiences both from previous year's administrations and in-year pre-post administrations. These shifts were attributable to programmatic changes museum educators (MEs) made, instigated by the first rounds of evaluation, rather than changes in teachers' stances. Thus, this article reports on the changes that MEs made in the program between Y1 and Y2 and the critical role that MEs play in supporting teachers' professional development and the ways in which their understanding/misunderstanding of teachers' needs drive programming. Herein the authors examine the influence of the assessment process on MEs' evolving understanding of their roles as teacher educators.