Using a randomized controlled trial, we investigated changes in both sexual harassment (SH) perpetration and victimization of 2104 middle school students in New York City who received divergent saturation and dosage levels of "Shifting Boundaries," an SH prevention program, which was represented by the length of the program. We assessed the saturation effect of the program by comparing the outcomes across respondents from 26 schools in which there were varying percentages of students enrolled in the program. The data suggested that, overall, the program was effective in reducing sexual harassment victimization but achieved a null effect against respondents' SH perpetration and that neither the length nor the school-saturation level of the program exerted a significant effect on SH perpetration. Although the data indicated a significant difference in SH victimization between the treatment and control group, when comparing subgroups who received treatment with divergent saturation and dosage levels, no statistically significant difference was identified. Our results suggested that the program effect was not contingent on the portion of students in a school who enrolled in the program, nor was it contingent on the dosage.