This study hypothesizes that course passing rates in remedial mathematics classes can be improved through early identification of at-risk students using a department-wide midterm, followed by a mandated set of online intervention assignments incorporating immediate and elaborate feedback for all students identified as "at-risk" by their midterm score. A sample of over 20,000 students was used to evaluate the intervention, which was implemented department-wide over several semesters in all developmental mathematics courses at a large diverse urban community college. The intervention was assessed by evaluating course passing rates (a proxy for passing rates on standardized exit examinations) and student time spent in the intervention lab. Students from semesters prior to the intervention were used as a control, with fall semesters compared to fall semesters and spring to spring, to control for possible variation in student enrollment. Highly statistically significant differences were found between student passing rates pre- versus post-intervention, with passing rates improving by as much as 50%. The size of this study and the diversity of the student population involved suggests that results are likely widely applicable to other institutions across the country. In particular, the interventions tested were chosen specifically because they can reasonably be implemented even across relatively large and diffuse departments with limited resources.