Screening and monitoring student reading progress can be costly and time consuming. Assessment embedded within the context of online instructional programs can capture ongoing student performance data while limiting testing time outside of instruction. This paper presents two studies that examined the validity of using performance measures from a computer-based reading program gathered through embedded "Assessment Without Testing®" technology as indicators of reading ability. These performance measures were strongly correlated with an established progress monitoring tool and a national outcome assessment. Assessment Without Testing® performance measures at beginning- and middle-of-year were also used to predict which students were likely to demonstrate proficiency on outside assessments at the end of the year. Considerations of using data gathered through technology-based instructional programs as a way to measure students' reading ability are discussed.