Research on the neurobiology of second language (L2) learning has historically focused on localization questions and relied on cross-sectional designs. Here, we describe an alternative paradigm involving longitudinal studies of adult, novice learners who are progressing through an introductory sequence of classroom-based L2 instruction. The goal of this paradigm is to determine how much L2 exposure is needed before learners incorporate L2 knowledge into their online comprehension processes, as reflected in scalp-recorded event-related brain potentials. Our preliminary studies show that some, but not all, aspects of the L2 (including lexical and morphosyntactic aspects) are incorporated into the comprehension system after remarkably little L2 instruction. We discuss the benefits of this paradigm while acknowledging the limitations and potential difficulties associated with it.