Heritage language (HL) research has investigated adults and children, while adolescents have garnered far less attention, despite adolescence being a crucial time in the development of idiolects and identities, and, hence, also for language maintenance. This study describes HL usage among Estonian-Swedish bilingual teenagers. Data were collected from 21 first- and second-generation Estonian heritage speakers (aged 12-17). Non-standard usage occurred in our corpus at low rates but was found across most speakers in certain areas of morphosyntax. We describe which factors drive such non-standard usage based on the example of two structures with more frequent non-standard occurrence: (1) object marking and (2) experiencer constructions with the verb meeldima 'to like/please'. Around 6% of objects were marked in divergent ways. Speakers employed two strategies for marking non-standard objects: case omission (i.e., using nominative and/or unmarked forms) and substitution (i.e., using non-target-like marking). Non-standard forms occurred in 11% of experiencer constructions. Speakers diverged more with marking the nominative Stimulus than the dative-like Experiencer, although both occurred in standard and non-standard forms. The reported usage patterns can be explained through the combined effect of cross-linguistic influence, simplification, and input frequency. We also tested the relation between non-standard usage and the speaker's sociolinguistic background, with mixed results. Considering the limited size and scope of the corpus, overall, the reported divergent usage patterns evidence the role of linguistic input and cross-linguistic effects.
