This study aims to exemplify how language teaching can benefit from learner corpus research (LCR). To this end, this study determines how L1 and L2 English speakers with diverse L1 backgrounds differ with respect to adjective amplification, based on the "International Corpus of Learner English" (ICLE) and the "Louvain Corpus of Native English Essays" (LOCNESS). The study confirms trends reported in previous research, in that L1 speakers amplify adjectives more frequently than L2 English speakers. In addition, the analysis shows that L1 and L2 English speakers differ substantially with respect to the collocational profiles of specific amplifier types and with respect to awareness of genre-specific constraints on amplifier use, and that even advanced L2 speakers tend to be unaware of stylistic constraints on adjective amplification because they model their academic output based on patterns generalized from informal conversation. These findings are useful for language teaching in that the data can be used to target L1-specific difficulties experienced by L2 English speakers.