We developed feedback on the quality of a synthesis text and tested the effects in an intervention study. Students compared their own text to scaled benchmark texts with annotations. The benchmarks were selected from our previous study, the national baseline. Students could compare their text to benchmarks with a similar score or to benchmarks with a higher score. We provided a detailed description on 4 important synthesis quality aspects: selection of information, integration of the sources, cohesion & coherence, and language use. The product-oriented feedback proved to be effective.