Designing professional development (PD) that helps teachers enact more ambitious math instruction that is responsive to emergent student thinking is challenging work. Two approaches to this sort of PD, practice-based professional development and lesson study, have different mechanisms for fostering change and choose different focus points for their efforts. Although there is substantial research support for each approach, each has limitations that can be characterized as "problems of enactment" (Kennedy, 1999) when used alone. This qualitative comparative case study examines what happened when these two approaches to professional development were used in tandem and given equal emphasis within the Responsive Math Teaching Project. It focuses on eight K-8 teachers participating in practice-based PD and collaborative lesson design, a derivation of lesson study, during the 2020-2021 school year in order to describe (a) take up, i.e., teachers' acceptance, adoption, and incorporation of ideas into their own classroom practice across both forms of PD, (b) barriers that arose and supports that helped mediate them, and (c) synergies, i.e., ways in which the Responsive Math Teaching Project's practice-based PD and collaborative lesson design were complementary and more impactful when used together than either might have been alone. This study adds to the literature by bringing to light the ways in which the affordances of each approach address the challenges inherent in the other and the take up that can result when the approaches are combined. Recognizing that professional development is a two-way street that involves active engagement on the part of teachers and responsive design on the part of those providing the PD, this study also examines how teachers invested their agency, the impact of that investment on their take up, and how PD structures fostered and leveraged that investment. By suggesting an expansion of Clarke and Hollingsworth's (2002) Interconnected Model of Professional Growth that includes the role of agency, this study provides an ideational resource for those planning and engaging in practice-based PD, lesson study, and combinations of the two. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]