The aims of this paper are to examine the measurement properties of the Reflection-in-Learning Scale (RLS) and to identify whether there are relationships between RLS scores early in the medical program and outcomes of the students' academic activity later on. The 14-item RLS was administered to second-year students (N=275) at start and at end of the third semester, after the students had reviewed their previous learning experience with the Course Valuing Inventory. The internal consistency, temporal stability and dimensionality of the RLS scores were investigated in relation to the start-end perspectives. Furthermore, a 2-year follow-up allowed the assessment of the relationships of third-term RLS scores with sixth-term measures of both academic achievement and diagnostic reasoning as appraised by the Diagnostic Thinking Inventory (DTI). Findings indicate that RLS data have acceptable unidimensionality and consistency of measurement, notwithstanding a significant individual-context interaction. Repeated measures revealed distinct patterns of RLS scores relating to perceived self-efficacy on the ability to reflect. Third-term RLS scores were significant, albeit weak, predictors of sixth-term cognitive achievement and DTI-related diagnostic reasoning ability. In conclusion, the results do not support a major explanatory role for RLS on knowledge representation. Nevertheless, the findings appear to substantiate the construct validity of this tool as an index of the students' frame of mind as regards reflective learning. They suggest that the RLS captures a self-regulation or cognitive housekeeping dimension of the students' reflective learning. The individual pattern of such (reflective) activity is likely to vary with specific learning conditions.