Research investigating improvisational skill development in adolescent learners is scant. In this study interviews with developing jazz improvisers are used to characterize the skill-building process. The findings were considered in light of two views of skill learning. In one view, students progress through several discrete levels, while in a different view students think like experts throughout development although the contextual demands vary. The six participants first improvised over a common 12-measure progression and then discussed their thinking in an interview that referenced their performance through approximate notation and audio recordings of their improvisation. Previous research with artist-level improvisers was used to develop an a priori coding frame to investigate to what extent the current participants described thinking that resembled that of experts. Results indicate that all six participants used monitoring and evaluation processes independent of skill level. However, only three participants with multiple years of jazz improvisation experience discussed how the underlying chord structure shaped their output. Also, experience level influenced the extent of planning during the improvisations, with novices thinking ahead a couple of notes while more experienced participants formulated plans for upcoming phrases and choruses. Pedagogical implications for improvisation in other music education settings are discussed.