In Spanish, voiced stops weaken to approximants and display variables degrees of lenition according to the context in which the stop occurs, making them a complex pronunciation feature. Accumulated findings from cross-sectional research on second language (L2) speakers suggests that many L2 learners struggle to produce the approximants even at the most advanced levels of study. The present study offers a new perspective on the approximants by studying individual learners’ production of Spanish [β] over time and across phonetic contexts. Twenty-six English speaking learners of L2 Spanish recorded two speaking tasks five times over a yearlong period corresponding to their second and third semesters of college-level language instruction. Mixed effects models were fit to learners’ C:V intensity ratio data to examine development, and stress and task type were included as substantive predictors. Although the group trajectory was flat, many learners displayed substantial change over time, including positive and negative trajectories.