This study measured the impact of the "Fitness Improves Thinking in Kids" ("FITKids") afterschool program on the executive control (i.e., maintaining focus, performing multiple cognitive processes) and physical fitness of preadolescent students. The "FITKids" program was held at the University of Illinois' campus and included 2 hours of afterschool activities each day. Study authors randomly assigned 221 students ages 7-9 to either participate in "FITKids" or to be in a business-as-usual comparison group. Executive control was measured before and after the "FITKids" program by assessing students' response accuracy and response time on two tasks: (1) attentional inhibition (flanker task) which required students to resist distracting information; and (2) cognitive flexibility (switch task) which required students to perform multiple cognitive duties at the same time. Study authors also measured fitness levels of students both before and after the intervention using body mass index (BMI) and maximal oxygen consumption during aerobic activity. The study authors found that the "FITKids" program increased accuracy in the attentional inhibition task and accuracy in the more difficult portion of the cognitive flexibility task. However, the What Works Clearinghouse (WWC) did not confirm this finding to be statistically significant after adjusting for multiple comparisons. The study also showed a statistically significant positive impact for one subscale of the attentional inhibition task, and the WWC confirmed this finding to be statistically significant. Additionally, the study authors found that "FITKids" had a statistically significant positive effect on aerobic fitness. Moreover, BMI for students in "FITKids" increased by a smaller amount than for students not in the program, and this result was statistically significant. The WWC confirmed the findings for aerobic fitness and BMI. The research described in this report meets WWC group design standards without reservations. A glossary of terms is included. The following are appended: (1) Study details; (2) Outcome measures for each domain; (3) Study findings for each domain; and (4) Supplemental findings for the executive control domain (flanker task). [The following study is the focus of this "Single Study Review": Hillman, C. H., Pontifex, M. B., Castelli, D. M., Khan, N. A., Raine, L. B., Scudder, M. R., Drollette, E. S., Moore, R. D., Wu, C-T, & Kamijo, K. (2014). Effects of the "FITKids" randomized controlled trial on executive control and brain function. "Pediatrics," 134(4), 1062-1071.]