Clahsen and Felser (CF) present a thought-provoking article that is likely to have a strong impact on the field, in particular, on developmental psycholinguistics and second language (L2) acquisition research. Unlike the majority of previous work on language acquisition that focused on "competence," that is, the knowledge basis underlying grammar, CF emphasize the need to approach language acquisition with psycholinguistic measures of processing. Based primarily on behavioral and electrophysiological on-line data, they argue that language acquisition in early first language (L1) and late L2 follows different patterns.