The primary goal of the study is twofold: to analyse definiteness and article use in spontaneous writing in Swedish by 12-year-old Finnish immersion students (n=142), and to compare that to the use by 15-year-old immersion students (n=162) and by 15-year-old non-immersion students (n=67). The analyses on the group level show that the 12-year-old immersion students usually do significantly better than the non-immersion group, and occasionally significantly better than the older immersion students. At the same time, the immersion students also have similar kinds of problems as non-immersion students, such as difficulty in choosing the right definiteness form.
Two for Finnish learners of L2-Swedish typical inaccuracies, i.e. omission of the indefinite article and overuse of the definiteness ending with certain definite pronominal attributes (e.g. the possessive and genitive ones) have, in contrast, been marginalized by the immersion method. The studied structures also show at the group level an order of acquisition similar to previous studies, explainable by both complexity hierarchy and cross-linguistic influence. Analyses on the individual level, however, show different orders of acquisition due to the criteria being used: systematic use favours frequent forms to the extent that a relatively complex form seems to be acquired prior to a rather simple, less frequent one.