This study employed ethnographic methods to describe and explain changes to beginning science teachers' (n = 6) practices and beliefs during a year long internship. Teaching practices were strongly influenced by the cooperating teachers. Initially, all six interns attempted to re-enact lessons they witnessed their cooperating teachers teach, including following lesson structures and borrowing representations, anecdotes, and jokes. Later, they independently implemented instruction that emphasized similar strategies as their mentors, regardless of whether or not they were experiencing success. Interns who were successful also shifted their beliefs to match their mentors. (Contains 4 tables.)