The Science Writing Heuristic (SWH) laboratory approach is a teaching and learning tool which combines writing, inquiry, collaboration and reflection, and provides scaffolding for the development of critical thinking skills. In this study, the California Critical Thinking Skills Test (CCTST) was used to measure the critical thinking skills of first year general chemistry students who were instructed using the SWH approach and first year general chemistry students who received traditional (TRAD) laboratory instruction. A quasi experimental pretest-posttest design involving the use of matched groups was used to assess differences in critical thinking between the two groups. Students in the SWH group had significantly higher total critical thinking scores over their traditional counterparts. The results indicate that the SWH approach shows efficacy in improving students' critical thinking skills over the traditional approach.