Working memory (WM), which includes short-term memory and cognitive control, has been found to be closely related to a wide range of high-level cognitive abilities and academic achievement. Prior studies showed children with attention-deficit/hyperactivity disorder improved their WM and fluid intelligence through computerized cognitive training (CCT) in a clinical setting. This research examined whether regular middle-school students would significantly improve their WM through CCT on WM; and if so, whether increase in WM would lead to improved fluid intelligence and science achievement. Two randomized pretest-posttest control-group experimental studies were conducted to answer these questions. Results showed CCT effectively improved regular students' WM in a school setting, with more increase in short-term memory than in cognitive control. No significant improvement was observed in fluid intelligence and science achievement immediately following training. Given the increasingly complex learning environment in schools, using CCT to improve students' cognition and academic learning has important implications for both practitioners and researchers in education.