The Science Writing Heuristic (SWH) laboratory instruction approach has been used successfully over a decade to engage students in laboratory activities. SWH-based instruction emphasizes knowledge construction through individual writing and reflection, and collaborative learning as a group. In the SWH approach, writing is a core component of learning. Previous studies on the SWH approach have reported effective implementation of the SWH approach leads to an improvement in overall student academic performance and content knowledge. Using a rubric developed by Maria Oliver-Hoyo, we compared the critical thinking (CT) skills of students across three groups, based on their written laboratory reports for various traits of CT, and the cognitive skills embedded in the rubric. Participants in this study were first-year general chemistry students who received traditional laboratory instruction, first-year general chemistry students who were instructed using the SWH approach, and fourth-year chemistry students who received traditional laboratory instruction. First-year students and fourth-year chemistry students who received traditional laboratory instruction scored statistically significantly lower on various CT traits, suggesting the SWH-based laboratory instruction is valuable in promoting CT thinking skills of students.