CAST created "Strategic Reader," a technology-based system blending Universal Design for Learning (UDL) and Curriculum-Based Measurement (CBM) in a digital learning environment to improve reading comprehension instruction. This experimental study evaluates the effectiveness of Strategic Reader using two treatment conditions for measuring progress (online vs. offline). Using both quantitative and qualitative data analysis, strong evidence is found that students using the online tool experience significant growth in comprehension scores. The difference in score growth in the online versus offline conditions is especially large for students with learning disabilities (LDs): Only in the online progress monitoring condition do LD students experience a statistically significant score increase. In addition, students with LDs report being substantially more engaged by (and with) Strategic Reader, finding many aspects of the tool differentially more helpful than their general education peers. In sum, the results provide promising paths for both curricular design and further research in the design of digital environments.