A court says Oklahoma DHS relied on the wrong law for nearly 20 years when it assessed parents 10 percent interest on certain child support accruals. In a published 1993 case, the state appeals court had determined that, when back child support in Oklahoma is accrued before a child support judgment is in place, interest is set according to the state’s Civil Procedure, which results in a significantly lower rate than the 10 percent assessed by law on delinquent child support.