Longitudinal research on second language (L2) sound learning demonstrates that speakers’ production of challenging L2 sounds can improve in the absence of targeted instruction. Although the growing body of longitudinal work on this topic provides insight into the rate and shape of development, the factors that shape L2 phonetic production in spontaneous speech are not yet well understood. The data described here are part of a longitudinal data set collected from native English speakers enrolled in introductory-level Spanish language courses. For the current analysis, 16 participants were selected based on the availability of data coinciding with the beginning and end of the first semester and end of the second semester. Participants completed a simplified picture description task. Voice Onset Time (VOT) was annotated and measured for all instances of Spanish /p, t, k/ in the speech samples. Participants’ instructors were recorded during two class periods. Recordings were transcribed and a frequency measure was calculated based on the resulting teacher speech data. After controlling for a range of linguistic factors known to affect VOT, modeling demonstrated that time and frequency were not significantly related to VOT.