This paper reports the findings of a four-year longitudinal study that examined the role of prior linguistic knowledge on the written L3 production of 93 Spanish/Catalan learners. Two research questions guided the study: the first asked whether a background language (L1s Spanish/Catalan, L2 German) would activate in parallel with L3 English during word construction attempts involving verbal forms, and if so, which would be the source language of blending. The second addressed the progressive readjustments of L2 activation and blending in the course of the first 200 hours of instruction. The elicitation technique was a written narrative based on a story telling task. Data were collected first when the learners were on average 9.9 years old (T1), and again at the ages of 10.9 (T2), 11.9 (T3) and 12.9 (T4). The focus of analysis was on word construction attempts that involved verbal forms. The results suggest that a background language, the L2, did indeed activate, especially at early stages of L3 acquisition.
