The purpose of this study was to compare the effectiveness of two kinds of reinforcements, tangible reinforcements and social reinforcements, on the academic achievement of eighth-grade female students with intellectual disabilities in the science subject. The study was an experimental method by pretest, with a control group. The participants of the study comprised 45 female students with intellectual disabilities from three different middle schools in the province of Tehran. The multistage cluster method was chosen to determine the sample. The Wechsler intelligence test for matching the groups in terms of IQ and teacher-applied tests were used for all students to measure the progress of students in science. Data were analyzed by one-way analysis of variance. The results showed that (a) there was a significant difference in the academic achievement scores of the groups after applying the intervention and (b) the mean difference in achievement scores for the tangible reinforcements group was significantly higher than the social reinforcement group and the control group. Also the mean scores for the social reinforcement group were significantly higher than the control group.