Recent calls for teacher preparation to become more grounded in practice prompt the questions: Which practices? and perhaps more fundamentally, what counts as a model of instruction worth learning for a new professional--i.e., the beginner's repertoire? In this report, we argue the following: If a defined set of subject-specific high-leverage practices could be articulated and taught during teacher preparation and induction, the broader teacher education community could collectively refine these practices as well as the tools and other resources that support their appropriation by novices across various learning-to-teach contexts. To anchor our conversation about these issues, we describe the evolution, in design, and enactment, of a "candidate core" and a suite of tools that supported the approximation of equitable and rigorous pedagogy for several groups of beginning science teachers. Their struggles and successes in taking up ambitious practice informed not only our designs for a beginner's repertoire but also a system of tools and socioprofessional routines that could foster such teaching over time. (Contains 3 figures, 1 table and 2 footnotes.)