The use of virtual design studios (VDS) in practice-based STEM education is increasing but requires further research to inform understanding of student learning and success. This paper presents a longitudinal, large-scale study (3 years, 3000 students) of student behaviour in an online design studio used as part of a distance learning Design and Innovation qualification, within the School of Engineering and Innovation at The Open University (UK). The sample size and time period of the study is unprecedented and provides unique insights into student behaviours. Moderate correlations between overall VDS use and student success were identified in early stages of study but were weaker in later stages. Detailed results identify specific behaviour correlations, such as 'listening-in' (viewing other students' work) and student success, as well as behaviour shifts from 'passive' to 'active' engagement. Strong intrinsic motivations for engagement were observed throughout and selected social learning mechanisms are presented to explain the empirical results, specifically: social comparison, presence, and communities of practice. The contribution of this paper is the framing of these mechanisms as steps in the longitudinal development of design students in a distance setting, providing an informed basis for the understanding, design, and application of virtual design studios.