There is considerable lab-based evidence for successful incidental learning, in which a learner's attention is directed away from the to-be-learned stimulus and towards another stimulus. In this study, we extend incidental learning research into the language learning classroom. Three groups of adult second language (L2) learners (N = 52) engaged in structured classroom Mandarin learning took part in an 8-week study. One group served as a classroom-only control group. The second group underwent additional intentional auditory training involving Mandarin speech and explicit feedback. The third group underwent additional incidental learning combined with nonspeech "perceptual building block" categories--categories that share critical perceptual dimensions with target L2 speech categories but that are not perceived as speech. We demonstrate that when supplemented with structured classroom learning, incidental learning involving nonspeech analogs promotes phonetic, category, and word learning equivalent to learning from more traditional intentional auditory training.