Distance learning programmes force us to reconceptualise the boundaries of time, place and process that structure traditional face-to-face forms of learning in higher education. We know that distance learning works and that assessment of student work is central to this process (Gikandi, Morrow and Davis, 2011). Online educators bring with them a collection of interrelated competencies to support distance learners’ academic achievements (Simonson, Smaldino and Zvacek, 2015), which can be evidenced in multiple ways in a professional learning context. While we know that formative and summative assessment share iterative and related diagnostic functions (Wiliam and Black, 1996), feedback as a key process supporting this is known to be differentially effective (Hattie and Timperley, 2007). To fully understand the potential of online formative feedback we must therefore investigate how feedback works in the online learning process. This paper explores statistical analyses of formative and summative assessment data from three cohorts of trainee teachers (n=1104) undertaking a Postgraduate Certificate in Education. It identifies the relationship between the grade achieved at the formative stage of an assignment and the grade achieved at the summative stage of the same assignment: in other words, the impact of formative feedback on summative outcomes. To contextualise the findings, patterns and themes in the data are highlighted to identify the use of a continuum of different levels of targeted feedback, ranging from feedback-as-elaboration to feedback-for-challenge, in line with Hattie and Timperley’s (2007) feedback questions.