This paper reports the results of a descriptive study on the use of a technology-enhanced formative assessment system called Accelerated Math (AM) for ELLs and their native-English-speaking (NES) peers. It was comprised of analyses of an extant database of 18,549 students, including 2,057 ELLs, from grades 1 through 8 across 30 U.S. states. These analyses were followed by semi-formal interviews with three teachers in California, Texas, and Minnesota, who use AM in mathematics instruction with ELLs and NESs. Without taking classroom-level information into account, ELLs, as a group, appeared to receive slightly greater implementation of this formative assessment system than did their native English speaking peers. Yet the results of five sets of generalized linear mixed-effects regression models indicated that, after accounting for classroom membership (or teacher effects), ELLs and their NES peers received roughly equal levels of implementation of the formative assessment system, suggesting that ELLs in this sample tended to be found in the classrooms of teachers who made somewhat greater use of their formative assessment system. The results of multilevel growth models suggested that ELLs tended to begin the school year with lower levels of mathematics skills, on average, than their NES peers. After accounting for variability associated with classroom membership, there were no significant differences between average growth in STAR Math scores between ELLs and NESs. Implementation of AM was a strong positive predictor of growth for both groups of students, yet there was a significant, but small, negative three-way interaction between ELL status, growth in mathematics, and implementation of AM. Teacher input, obtained in semi-formal interviews, added perspective to the results of quantitative analyses of implementation and growth. Their responses to questions about patterns of implementation or observations of growth in STAR Math scores provided illustrations of trends encountered in statistical models, and suggested issues for consideration in future research on the topic of formative assessment practices in mathematics for ELLs. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]