Relatively little is known about how working students manage their dual roles of work and study. To extend this research, we examined the direct and indirect relationships between boundary flexibility-ability (the appraised capacity to modify a boundary of one role to accommodate better the demands of another role) and boundary flexibility-willingness (the preparedness to do so) in both the work and study domains and outcomes of student burnout and study engagement in a sample of 851 working students (76% female; mean age 20.69 years). We tested the indirect paths via work-study conflict and facilitation. Both work and study flexibility-ability and flexibility-willingness, independently and in concert, were related to student burnout (46% variance explained) and study engagement (28% variance explained) as expected, and results supported work-study conflict and facilitation as underlying mechanisms in these relationships, with the indirect path via work-study conflict being more important than that via work-study facilitation. Thus, there are benefits for students when work and study boundaries are flexible and when students are willing to make use of this flexibility.