In a pilot study of the Technology Immersion model, high-need middle schools were "immersed" in technology by providing a laptop for each student and teacher, wireless Internet access, curricular and assessment resources, professional development, and technical and pedagogical support. This article examines the fidelity of model implementation and associations between implementation indicators and student achievement. Results across three years for 21 immersion schools show that the average levels of school support for Technology Immersion and teachers' Classroom Immersion increased slightly, while the level of Student Access and Use declined. Implementation quality varied across schools and classrooms, with a quarter or fewer of schools and core-content classrooms reaching "substantial" implementation. Using hierarchical linear modeling, we found that teacher-level implementation components (Immersion Support, Classroom Immersion) were inconsistent and mostly not statistically significant predictors of student achievement, whereas students' use of laptops outside of school for homework and learning games was the strongest implementation predictor of achievement. (Contains 14 tables, 5 figures, and 3 endnotes.)