Constraints in resourcing and student dissatisfaction with assessment feedback mean that the effectiveness of our feedback practices has never been so important. Drawing on findings from a three-year study focused on student engagement with feedback, this paper reveals the limited extent to which effectiveness can be accurately measured and challenges many of the assumptions and beliefs about effectiveness of feedback practices. Difficulties relating to multiple purposes of feedback, its temporal nature and the capabilities of evaluators reveal that measuring effectiveness is fraught with difficulty. The paper argues that the learner is in the best position to judge the effectiveness of feedback, but may not always recognise the benefits it provides. Therefore, the pedagogic literacy of students is key to evaluation of feedback and feedback processes.