Although open educational resources (OERs) can help bridge high-school – university vocabulary gaps, optimal utilization of OERs requires effective self-directed learning. This bi-national two-year study adopted a design-based research paradigm to collect Chinese university students' (n = 358) perceptions regarding design factors that support self-directed vocabulary learning in mobile learning environments (MLEs). Results showed that additional scaffolding after Year One in the form of L1 translations of high-frequency academic words significantly correlated with improved performance on basic level vocabulary exercises and pop quizzes. However, results suggest that moving mobile learning into the mainstream will require (1) design features that provide additional scaffolding for more complex vocabulary learning, (2) clearer guidelines for students on integrating desktop and mobile devices and (3) ongoing guidance from teachers to develop students' capacity for self-directed learning to ensure optimal benefit from independent study of vocabulary OERs.