This exploratory study, undertaken from a socio-cognitive perspective, aims to investigate the effects of intensive preparatory high school training in L1 and/or L2 essay writing for university entrance exams. The analysis focuses on the task response and structural features in L1 (Japanese) and L2 (English) essays written by first-year Japanese university students (N = 28). The results reveal that the L1 intensive training emphasized the importance of establishing clarity and demonstrating originality for the sake of gaining the reader's approval, whereas the L2 training stressed the need to take a clear position on an issue and include a position statement at the beginning of an essay. Moreover, the interaction between intensive L1 and L2 training was found to reinforce the students' tendency to apply the meta-knowledge they had acquired to their L1 and L2 essay writing. In some cases, undergoing both kinds of training promoted a sense that writing in L1 is different from writing in L2, whereas in other cases, it led to a perception of L1 and L2 writing as being the same. The findings provide evidence for transferability of writing competence across languages.