Here we report findings from a cross-sectional study of morphosyntactic processing in native German speakers and native English speakers enrolled in college-level German courses. Event-related brain potentials were recorded while participants read sentences that were either well-formed or violated German subject-verb agreement. Results showed that grammatical violations elicited large P600 effects in the native Germans and learners enrolled in third-year courses. Grand mean waveforms for learners enrolled in first-year courses showed a biphasic N400-P600 response. However, subsequent correlation analyses revealed that most individuals showed either an N400 or a P600, but not both, and that brain response type was associated with behavioral measures of grammatical sensitivity. These results support models of second language acquisition which implicate qualitative changes in the neural substrates of second language grammar processing associated with learning. Importantly, we show that new insights into L2 learning result when the cross-subject variability is treated as a source of evidence rather than a source of noise.