The topic of this article is the link between research on the neurocognition of the teaching--acquisition interface and research on second language teaching. This recent scientific enterprise investigates whether and how different aspects of second language instruction may change both the anatomy and the functioning of an adult learner's brain even in a short period of time. In this article, I analyse how neurolinguists have operationalized three aspects specifically related to second language teaching: (1) learners' proficiency; (2) the between-groups experimental design; (3) the implicit vs. explicit teaching dichotomy. I suggest that the degree of replicability of such neurolinguistics studies can be increased by adopting non-circular operational definitions. Such definitions should not be based on psycholinguistic or neurolinguistic metrics, but on standards that are commonly discussed in the literature on instructed second language acquisition, second language teaching, and assessment. Finally, I suggest that for future research neurolinguists should consider the advantages of welcoming on board more developmental linguists and teachers.