The authors investigated the effects of intrinsic and extrinsic motivation on reading achievement for urban middle school students. The authors initially developed a research-based theoretical model representing interrelationships among students' ethnicity, gender, grade level, intrinsic motivation, extrinsic motivation, and reading achievement. When the authors tested the model, structural equation models (SEMs) produced effects that were statistically significant. For example, a multiple-groups SEM analysis indicated that intrinsic motivation had a stronger positive relationship with reading achievement for Asian students than for Hispanic students. Analysis by gender, ethnicity, and grade level showed statistically significant decreases over time for intrinsic and extrinsic motivation. Results suggest a significant decline in overall motivation to read during the middle school years for students in urban schools. (Contains 5 figures and 6 tables.)