Many heritage speakers (bilinguals in a minority language context) turn to the second language (L2) classroom to expand their knowledge of the heritage language. Critical questions arise as to how their linguistic knowledge compares to that of post puberty L2 learners. Focusing on recent experimental research on grammatical domains typically affected in both L2 learners and heritage speakers, this article addresses whether exposure to the family language since birth even under reduced input conditions leads to more native-like linguistic knowledge in heritage speakers as opposed to L2 learners with a later age of acquisition of the language, how differences in input and language learning experience determine the behavioral manifestations of linguistic knowledge, and whether formal instruction in the classroom is beneficial to heritage speakers. It is argued that the extension of theoretical frameworks and methodologies from SLA has significantly advanced the field of heritage language acquisition, but deeper understanding of these speakers will also need more fruitful integration of the psycholinguistic and sociolinguistic factors that contribute to the acquisition and maintenance of heritage languages.