Syntactic knowledge, the implicit and explicit knowledge of syntax, is a necessary--but often overlooked--component of proficient reading (e.g., Deacon & Kieffer, 2018). Though some research exists on effective syntactic instruction, such as sentence combining (Neville & Searls, 1985; Wilkinson & Patty, 1993), researchers have called for additional investigations (e.g., MacKay et al., 2021). The purpose of this quasi-experimental, mixed methods study was to explore the effectiveness of a syntax-focused reading intervention on middle-school students' syntactic knowledge, in comparison with an alternate condition group. In this study, which took place over nine weeks, 49 sixth graders in a Literacy Support class were assigned to the syntax-focused reading intervention group or the alternate condition group receiving comprehension strategy instruction. The author analyzed the quantitative data using ANCOVA tests with performance on two measures of syntactic knowledge as the outcome variables. The results indicated that there was no significant difference in students' overall performance on the two measures of syntactic knowledge. However, students in the syntax-focused reading intervention group performed significantly better on items in one measure that targeted knowledge of appositive phrases. This finding suggested that students may have used their explicit knowledge of appositive phrases, learned in the syntax-focused reading intervention, to determine the meaning of unknown words in connected text. Qualitative analyses of individual and focus group semi-structured interviews conducted with six students from both groups (n = 12) suggested that the syntax-focused reading intervention was effective at developing students' metalanguage and strategies for breaking apart sentences, which ultimately supported their syntactic knowledge. [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.]