The Science Teaching Experience Program--Working in Science Education (STEP-WISE) provides teaching experience for postdoctoral scholars holding full-time research appointments. Through a combination of mentorship, deliberate practice, and feedback, the postdocs learn and apply inclusive, evidence-based pedagogies. STEP-WISE is integrated into postdocs' demanding schedules and is sustainable for institutions to run. Here, we assess the effectiveness of STEP-WISE. We used the Classroom Observation Protocol for Undergraduate STEM instruction to quantify instructor and student behaviors in 20 STEP-WISE class sessions from seven courses designed and taught by postdocs in the program. We found that all of the postdocs used student-centered teaching strategies. Also, using a design-based research framework, we studied the program to identify the salient components of its design. Four interconnected key elements contribute to the program's success: (1) two training sessions, (2) a precourse meeting with the mentor, (3) implementation of active-learning strategies with support, and (4) debriefing with the mentor after each class session. STEP-WISE is a replicable model to support postdocs seeking training and experience in evidence-based teaching practices geared to improving undergraduate education and transforming pedagogical practice. We conclude that high-impact teaching can be learned early in a career with streamlined training and intensive mentoring.