There is increasing interest in how educational technologies can be used to promote and create meaningful learning opportunities and, more specifically, how social media tools can be harnessed to encourage language learning through online interactions. Educational social media tools, however, thrust student learning from a private space into a public one and raise ethical concerns regarding digital surveillance. Drawing from Norton's (2013) conceptualisation of language investment and identity and Bourdieu's (1990) thinking tools of habitus and field, this paper explores the attitudes and experiences of 30 Japanese exchange students studying at a high school in Australia, as they engage with the educational social media platform, Edmodo. This action research study aimed to encourage language investment by providing an online space for students to develop their English language identities in and amongst their Japanese peers. However, this study found that many of the participating students resisted and/or disliked using Edmodo because they felt restricted by the platform, highlighting the need for students to have a sense of autonomy in the midst of teacher control and surveillance. Additionally, this study reveals that the students who engaged regularly, and without the prompting of the teacher, were students who were academically stronger, suggesting that students' self-efficacy is closely linked to language investment and the willingness to develop their language identity.