Criticizing the common approach of supporting peer assessment through providing assessors with an explication of assessment criteria, recent insights on peer assessment call for support focussing on assessees, who often assume a passive role of receivers of feedback. Feedback requests, which require assessees to formulate their specific needs for feedback, have therefore been put forward as an alternative to supporting peer assessment, even though there is little known about their exact impact on feedback. Operationalizing effective feedback as feedback that (1) elaborates on the evaluation, and (2) to which the receiver is agreeable, the present study examines how these two variables are affected by feedback requests, compared to an explanation of assessment criteria in the form of a content checklist. Situated against the backdrop of a writing task for 125 first-year students in an educational studies program at university, the study uses a 2x2 factorial design that resulted in four conditions: a control, feedback request, content checklist, and combination condition. The results underline the importance of taking message length into account when studying the effects of support for peer assessment. Although feedback requests did not have an impact on the raw number of elaborations, the proportion of informative elaborations within feedback messages was significantly higher in conditions that used a feedback request. In other words, it appears that the feedback request stimulated students to write more focused messages. The use of a feedback request did, however, not have a significant effect on agreement with feedback.