This study investigated the effect of immediate, corrective feedback delivered via an advanced online technology on the ESL teachers' instructional practice and their students' academic performance. The study used an A-B-A baseline design and the participants included three teachers and their students enrolled in one selected class from each teacher. Data collected included teacher practice measured by three-term contingency trials, student behavior measured by number of correct responses, and teachers' perceptions of the experience with receiving immediate, corrective feedback through online technology. Results indicated that the corrective, immediate feedback was an effective way to increase completion of three-term contingency trials by teachers and to increase the correct responses by students. All teachers acknowledged the benefits of the immediate, corrective feedback and rated the online technology as non-intrusive. Implications for teacher educational research and practice are discussed.