The purpose of this mixed-methods study was to examine the relationship between science writing and student science achievement and how teachers implement the writing strategy claim, evidence, and reasoning (CER) in their science classrooms. Writing is a critical tool for scientific literacy and student achievement. We must teach our students to write well. To accomplish the study, twenty-five science teachers from five high schools of a large urban school district located in southeast Texas participated in the study. The study provided significant results of students' achievement in science by the implantation of writing CER in science classrooms. Nine teachers from two schools where the researcher served, participated in the semi-structured interviews regarding the implementation of the CER writing framework in their science classrooms. Interviewees' responses revealed that teachers showed positive perceptions regarding CER, CER training, and its implementation in science classrooms. [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.]