The purpose of this study was to ascertain the ways former professional scientists who are learning to become teachers understand the planning and implementation of instructional design 1) while they are in a university program learning to become teachers and 2) during their first year of full-time teaching in a secondary classroom. The study used a grounded theory approach and was informed by multiple classroom observations, lesson planning artifacts, and interviews. It was found that during their methods class the teacher candidates employed both student-centered and backwards design principles. However, once the teacher candidates started teaching full-time, they no longer designed instruction and instead adopted lesson plans from veteran teachers, adapting only small parts to become more student-centered.