Novice teachers improve substantially in their first years on the job, but we know remarkably little about the nature of this skill development. Using data from Tennessee, we leverage a feature of the classroom observation protocol that asks school administrators to identify an item on which the teacher should focus their improvement efforts. This "area of refinement" overcomes a key measurement challenge endemic to inferring from classroom observation scores the development of specific teaching skills. We show that administrators disproportionately identify two teaching skills when observing novice teachers: classroom management and presenting content. Struggling with classroom management, in particular, is linked to high rates of novice teacher attrition. Among those who remain, we observe subsequent improvement in these skills.