This project will significantly improve opportunities for learning experienced by all students in large enrollment introductory STEM courses. Too often, undergraduate introductory STEM courses are offered in 100+ seat lecture halls where student engagement in the hard work of learning new information, as opposed to simply listening to an expert talk about it, is the exception rather than the rule. Many undergraduates entering STEM majors need help in learning how to learn, especially in large enrollment classes with challenging STEM content. This project will change this situation. Using large classrooms recently redesigned for small group collaborations, this project will use evidence from research on learning, teaching, and assessment to create and refine a model for training teams of STEM instructors and their instructional assistants as learning leaders. All students in the collaborative learning environments, with guidance and support from the instructional team, will have opportunities to learn STEM in collaborative, task-oriented classes. Simultaneously, students will learn how to learn STEM in an environment which likely resembles the work environment of their future professional careers. This project will generate a professional development model that improves instructional team members' abilities to practice evidence-based instruction in large enrollment undergraduate STEM collaborative learning environments (CLEs). The quality of instruction and assessment practiced by these teams is an important aspect of successful student learning in large enrollment CLEs. Each team will be comprised of four roles: (1) a lead instructor, a faculty member who will be the primary instructor, curriculum planner, and developer of learning tasks; (2) a learning assistant trainer, a faculty member who will train learning assistants on evidence-based practices for engaged student learning; (3) assessment coaches, experienced learning assistants who will serve as lead assessors of student engagement by monitoring and supporting learning coaches' formative assessment practices and feedback providers to lead instructors and learning assistant trainers; (4) learning coaches, learning assistants who will directly engage with students and provide formative assessment. The project will build upon research on learning task quality, formative assessment practices, and student-assisted teaching, which suggests that productive student learning in large enrollment CLEs: (1) requires engagement with appropriately challenging, high quality learning tasks, (2) is fostered with evidence-based formative assessment practices, and (3) involves efficient functioning of instructional teams prepared to support student learning with evidence-based practices. Built upon these premises, the project's professional development activities will build instructional team members' abilities to succeed in their roles. Research goals are to: (1) track changes in task quality, formative assessment practices, and instructional team performance over several semesters within six to nine large enrollment CLEs, and (2) document and describe the challenges associated with achieving the desired evidence-based practices of task development, formative assessment, and instructional team performance using, and annually revising, the professional development model.