Writing-to-Learn in High-School Chemistry: The Effects of Using the Science Writing Heuristic to Increase Scientific Literacy The purpose of this study was to investigate the effectiveness of using the Science Writing Heuristic (SWH) as an instructional tool to improve academic achievement and writing in the context of scientific literacy. This quasi-experimental study compared the effects of using the SWH in five laboratory settings over a 16-week span. The SWH was administered to a treatment group (n = 63), whereas the comparison group (n = 67) received laboratory sessions using a traditional laboratory report format. There were four classes (n = 130) of general chemistry enrolled in the study with two teachers. Each teacher taught a treatment and comparison class during the study. A pretest was administered to investigate any between-group mean differences. There was no statistically significant difference in between-group mean differences. The dependent measures administered to investigate differences between the treatment and comparison group included five SWH laboratory scores, a posttest content assessment (CA), a posttest written assessment (WA), and a student perceptions questionnaire. Teacher interviews were conducted as anecdotal evidence of teachers' opinions about the use of the SWH compared with a traditional laboratory format. The means on the CA and the WA were higher in the treatment group than the comparison group. Two independent-samples t tests were conducted to compare the means of the CA and the WA by treatment and comparison groups. Ten paired-samples t tests were used to make planned pairwise comparisons between the laboratory scores. There were five statistically significant differences in laboratory scores; however, there was no clear linear trend of an increase in means over time. There were no statistically significant differences in the posttest CA or posttest WA. There was a statistically significant difference in one of the student-perceptions-questionnaire components focused on writing as a tool for learning chemistry. The results favored the traditional laboratory format group. Post-hoc data analyses were conducted due to treatment fidelity concerns. A statistically significant difference in means was found between a treatment and comparison class through the post-hoc analyses. Additional research may be conducted on professional development to support teachers in implementing the SWH with fidelity. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]