Integrating computing and mathematics appeals to various stakeholders for a variety of reasons. For the mathematics education community, computing offers an application of mathematics concepts that may strengthen teachers' and students' mathematical understanding; for the computer science (CS) education community, integration enables equitable access to computing education for all students; for state boards and districts, integration accommodates staffing and curricular constraints while targeting core learning objectives in multiple disciplines. Bootstrap is a nationally-deployed curriculum that integrates computer science and algebra. Bootstrap's current professional development (PD) program for math teachers is a 3-day in-person event which assumes that teachers are somewhat facile with algebraic functions. Both Bootstrap and the National Council for Teachers of Mathematics (NCTM)  have observed that some teachers have a weak command of functions. School districts would prefer a shorter in-person PD to reduce staffing costs and increase flexibility. This project will use a hybrid PD model to address both needs. Simultaneously, the project will research ways to tailor the online content to be effective for teachers who differ in their understanding of functions, goals for pursuing PD, and interest in mathematics, computing, math/CS integration, and student thinking. This Researcher-Practitioner Partnership team includes Bootstrap; NCTM (specifically its Math Forum team, which has expertise in on-line training); Brown University; Swarthmore College; the Oklahoma State Division of Secondary Mathematics and Computing Education and school districts in Texas. A total of 270 middle-school math teachers---a majority from rural areas or serving Native American or Hispanic students in our partnering regions---will participate in Bootstrap PD under this project. Assuming typical adoption rates, these teachers should reach 6,000 students within the project period alone. Building Bootstrap content into the Math Forum will expose thousands of NCTM's teachers to the potential of integrated math/CS curricula. The team will use design-based research to develop and deploy a hybrid PD model and online support community for Bootstrap teachers, augment Bootstrap PD to reinforce teachers' understanding of algebraic functions, and conduct quasi-experimental studies to inform the design of different pathways through the PD. This project will study how to develop teachers' understanding of CS while also strengthening their math proficiency. In particular, the project will explore the possibilities for CS to improve teachers' understanding of algebraic functions. The project also will study ways in which teachers' interest can be made visible and useful in improving engagement and learning in integrated CS and mathematics PD. The results should apply to integrative programs beyond Bootstrap, suggesting strategies to tailor PD to serve more teachers.