Effects of informal digital learning of English on EFL learners’ writing skills: a mixed-methods study

Informal digital learning of English (IDLE) is increasingly positioned as a meaningful extension of classroom instruction in EFL settings, yet intervention-based evidence for L2 writing development remains limited. This mixed-methods study investigated the effect of teacher-supported IDLE on Iranian university students’ L2 writing performance and their perceptions of how IDLE supported their writing development. Following proficiency screening and random group allocation, 42 Iranian undergraduate EFL learners completed a pre-test, an immediate post-test, and a delayed post-test four weeks after a 16-week intervention. Both groups received comparable weekly in-class writing instruction; the IDLE group then engaged in structured, teacher-supported out-of-class digital writing activities, while the control group completed parallel teacher-led writing practice in class. Covariate-adjusted analyses indicated that the IDLE group achieved significantly greater writing gains than the control group at both post-test points, with improvements sustained after the intervention. Qualitative analysis of reflective essays further clarified the learning mechanisms underlying these gains, highlighting unlimited access to authentic resources and audiences, strengthened autonomy and locus of control, and improved affective engagement. These findings establish teacher-supported IDLE as a causally effective intervention for L2 writing development and identify the specific mechanisms – resource access, learner autonomy, and motivational support – that make digital writing engagement productive beyond the classroom.