The present study investigated the effects on student test scores of providing Tier 1 and Tier 2 professional development (PD) about language arts instruction to teachers at a Title I elementary school. All general education teachers received ongoing feedback and assistance in hands-on learning of effective instructional techniques for reading, spelling, and composition over 4 school years. The PD gradually advanced and built upon itself. Hierarchical Linear Modeling designs and split-plot within-subjects contrasts were used to compare student scores on several measures before and during PD. Findings indicated that PD had a significant effect on most of the measures. Student performance relative to other schools demonstrated that scores were best at the end of the study after PD in both Tiers. The current study adds to the evidence that effective teacher training can result in powerful benefits for students. [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.]