In evaluating the success of teacher development programs, valid and scalable measures of teaching practice are needed. We have developed and validated the Science Lesson Plan Analysis Instrument (SLPAI) for quantitative evaluation of teacher-generated multiday lesson plans. This paper presents the SLPAI as a complement to surveys and classroom observation, and demonstrates its use in 2 pilot studies. The SLPAI was used formatively to measure the teaching practices of incoming program cohorts and tailor program instruction. It was also used to track changes in teaching practice and pedagogical knowledge of participants over time, providing summative evidence of program effectiveness. (Contains 10 tables, 1 figure, and 7 footnotes.)