Some 93 members of Congress requested the review back in 2015 after the New York Times published articles about the "rampant" sexual abuse of children by members of the Afghan military and police forces.
SIGAR found that despite DoD and the State Department's knowledge of confirmed human rights violations among Afghan security forces, the Secretary of Defense has used a clause in DoD's Appropriations Act that continues to provide them funding for select training, equipment, and other assistance — bypassing Leahy law compliance.
Invoking the clause does not require Congressional notification, and Senate Appropriations Committee has since worked to remove the clause from the FY18 Defense Appropriations Bill.
DoD has provided funds to twelve Afghan security force units implicated in fourteen gross violation of human rights incidents in 2013, SIGAR said. Nine additional units received funds with some exceptions of how that money can be used.
"Two service members who reported directly observing or hearing what they believed to be evidence of child sexual assault by Afghan security forces said they did not receive training on how to address sexual abuse of children by Afghan security forces if they encountered it," SIGAR said.
A third service member interviewed by SIGAR said it was well known on his base that sex occurred between boys and Afghan National Police personnel.
"While he and his fellow service members talked and laughed about it, he added, they did not take action to report it," SIGAR said.
When given an opportunity to respond to SIGAR's report, DoD said U.S. Forces Afghanistan's Legal Office provides weekly training to all newly-arriving military personnel, government employees, and contractors, but that the department will "reinforce the importance of training on human rights abuse reporting, including suspected child sexual assault."
DoD also told SIGAR that it would establish a single tracking system for gross violations of human rights incidents. Without a single tracking system, SIGAR said there was "confusion" among parts of DoD as to who implemented the Leahy Law in Afghanistan.
In a statement to ABC News, the State Department thanked SIGAR for its report, and said they will continue to impress on the Afghan government at the highest levels the importance of more effective action to prevent these practices.
"We have long been aware of the challenges that SIGAR highlights in its report, and strongly condemn any violation of human rights, particularly child sexual assault and the practice of bacha bazi in which men exploit boys for social and sexual entertainment," the State Department said.
ABC News' Conor Finnegan contributed to this report.