The main aim of the present paper is to introduce a model for digital game categorization suitable for use in English language learning studies: the Scale of Social Interaction (SSI) Model (original idea published as Sundqvist, 2013). The SSI Model proposes a classification of commercial off-the-shelf (COTS) digital games into three categories: singleplayer (the smallest scale), multiplayer, and massively multiplayer online games (MMOs, the largest scale). The potential for naturalistic learning (Benson, 2011) of English is hypothesized to be greater the larger the scale of in-game social interaction. A secondary aim is to present preliminary findings regarding the validation of the SSI Model based on data collected from Swedish learners (9th grade) in an ongoing 3-year study about the relation between out-of-school digital gameplay and vocabulary acquisition. The results reveal, for example, that it is more common that learners who play games frequently play multiplayer games and/or MMOs than singleplayer games. Moreover, the results provide partial evidence of the validity of the SSI Model in that the learners who are categorized as playing multiplayer games and MMOs score higher on two vocabulary tests than the learners categorized as playing singleplayer games. [For full proceedings, see ED565044.]