Think Through Math (TTM) is an online, adaptive mathematics program designed to supplement classroom instruction. The program is funded by the Texas Education Agency (TEA) for students in grades 3-8, and schools have 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 2013-2014 with the results of similar students in the same grades who did not use TTM. Three treatment groups of students were considered: all TTM users in the district, TTM users in 2013-2014 priority and focus schools, and TTM users who took the June 2014 retest of the STAAR mathematics test. Some of the highlights are as follows: (1) Students in every grade level in HISD used TTM in 2013-2014 and 95 percent of the TTM users were in grades 3-8. 29,359 TTM users and 25,718 non-TTM users met the criteria for inclusion in this study, for a total of 55,077 students included in the analyses; (2) Propensity score analyses were used to compare the mathematics achievement of TTM users matched with non-TTM users. Results indicated that HISD students who used TTM had significantly higher 2014 STAAR scale scores than did matched students who did not enroll in the program; (3) TTM users at priority and focus schools who were matched with non-TTM users at the same schools were also found to have obtained significantly higher 2014 STAAR mathematics scale scores than non-TTM users had; (4) For students who took the June 2014 STAAR retest, however, there were no significant differences in scale scores earned by TTM users when compared with the results of matched non-TTM users; and (5) Regression analyses indicated that for most groups of students, passing a higher number of TTM lessons, particularly passing a higher number of target TTM lessons, predicted a higher 2014 STAAR mathematics scale score. Effect sizes for the significant relationships were small, with the exception of a moderately strong relationship between the number of TTM target lessons passed and 2014 STAAR mathematics scale scores for students who met the phase-in 1, satisfactory standard on the 2013 STAAR mathematics assessment. Recommendations, and Administrative Response are provided.