Think Through Math (TTM) is an online, adaptive mathematics program designed to supplement classroom instruction. In 2014-2015, the program was funded by the Texas Education Agency (TEA) for students in grades 3-8, and schools had the option to purchase the program for students in other grades. This report compares the STAAR mathematics achievement of HISD students in grades 3-8 who enrolled in the TTM program in 2014-2015 with the results of similar students in the same grades who did not use TTM. Comparisons were made for students districtwide, for students based on 2014 STAAR Mathematics performance level, and for students who attended a 2014 Improvement Required (IR) school. Key findings include: (1) A total of 43,997 HISD students used TTM in 2014-2015. Nearly all the students, 99 percent, were enrolled in grades 3-8, the grade levels for which the program was supported by TEA; (2) Students enrolled in TTM completed an average of 14 TTM lessons and passed an average of four on-grade level lessons in the academic year; (3) Propensity score matching, which matched TTM users with non-TTM users based on key variables, indicated no significant difference in 2015 STAAR Mathematics scale scores between TTM users and non-TTM users; and (4) Propensity score matching was also used to confirm that there were no significant differences between TTM users and non-TTM users based on 2014 STAAR Mathematics performance or enrollment in an IR school. Specifically, there were no significant differences in 2015 STAAR Mathematics scale scores of matched TTM and non-TTM users who did not meet the 2014 STAAR Mathematics standard, who met but did not achieve the advanced 2014 STAAR Mathematics standard, who met the 2014 STAAR Mathematics advanced standard, or who attended a 2014 IR school. Recommendations and administrative response are provided.