In engineering fields, students are expected to construct technical arguments that demonstrate a discipline's expected use of logic, evidence, and conventions. Many undergraduate bioengineering students struggle to enact the appropriate argument structures when they produce technical posters. To address this problem we implemented Calibrated Peer Review™ (CPR), a web-based tool, to help students improve their scientific reasoning and critiquing skills. In 2007 bioengineering students in a tissue culture laboratory course constructed technical posters presenting their experimental methods, results and conclusions. The posters were uploaded into CPR, which permitted a highly structured approach to peer review. During the calibration, peer-critiquing and self-evaluation stages, students and the instructor responded to 15 statements about each poster's technical content and visual appeal. These statements ranged in cognitive complexity from knowledge to evaluation (Bloom, Englehart, Furst, Hill, & Krathwohl, 1956). Our analysis of the CPR data shows that trained peers' holistic ratings of posters are linearly correlated with instructor ratings (r = 0.6). In peer review, students also demonstrate expert skills, as compared with the instructor, on low-level cognitive tasks such as knowledge of material. However, students routinely overrated their peers' posters and their own as compared to the instructor on high-level cognitive tasks such as evaluation. Student self-evaluations also do not correlate well with instructor evaluations on a holistic scale (r = 0.17). CPR has therefore enabled us to identify where our students are having the greatest difficulty evaluating technical arguments.