There has been a long, historical debate around the relevance of grammar instruction on writing development. The grammar wars continue to contest literacy experts (Andrews, et al., 2006; Myhill & Watson, 2014), and a best instructional approach for teaching grammar remains unspecified. The purpose of this quantitative study was to investigate a guided apprenticeship approach for teaching grammar and examine whether this method of instruction related to student performance or the application of grammar skills to new contexts in any manner as compared to students who received instruction through traditional methods using an isolated units' approach. Two quantitative measurement tools were used in this study, the PA Classroom Diagnostic Tools (CDT) and a researcher-designed writing protocol. Data was collected during a district-initiated year-long pilot, in fourth-grade English Language Arts (ELA) classrooms in a large suburban school district in northeastern Pennsylvania. Three English Language Arts (ELA) Treatment classrooms received grammar instruction via the guided apprenticeship approach, and three Control classrooms received instruction with traditional isolated units' methods. Key findings of the study were: (1) Analysis of the CDT data indicated that the Treatment group who received instruction by the guided apprenticeship approach showed a higher percentage of students scoring at the proficient level, resulting in gains from the BOY to MOY for all three diagnostic categories, (2) Analysis of the Control group's CDT data indicated mixed results for students who received grammar instruction through an isolated units' approach. Gains were made in two of the diagnostic categories, however, the Control MOY group experienced a slight decrease in percentage score for one diagnostic area, (3) Analysis of CDT data indicated that students in the Treatment group made higher overall improvements than the Control group from BOY to MOY, and (4) Data results of student writing samples reported through t-tests, descriptive statistics, and narrative indicated that the guided apprenticeship approach to grammar instruction did not result in statistically significant differences in the student application of grammar skills to new contexts as measured by the researcher-designed writing protocol. Given the results of this study, further study around the guided apprenticeship approach for grammar instruction would be warranted. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]