This mixed-methods, quasi-experimental, bounded case study of eighth graders in one middle school explored the use of sentence starters within online discussion forums as a pedagogical tool to promote critical thinking as students analyzed literature and socially constructed meaning. Sentence-starters featuring the language of critical thinkers were provided as an interactive link within the student forums. A statistically significant relationship was found between the use of the critical thinking language and the participation and critical thinking levels of student responses. The experimental group used the scaffolding significantly more often than the control group. Although qualitative data revealed positive effects of the scaffolding, statistically significant differences between the experimental and control groups' participation and critical thinking levels were not found. Over the course of the experiment, participation levels decreased and critical thinking levels did not change significantly over time. Lack of power to detect differences may explain the inconsistent results.;Interest and difficulty level of the content and peer interaction were found to be key variables in influencing student responses along with teacher expectations and classroom follow-up.