Though measures of long-term academic performance trends are valuable to education policy analysts and policymakers, they have been hard to come by at the state level, where most education policy is made. Such data are either nonexistent prior to 1990 or are unrepresentative of statewide student populations. A continuous series of state mean SAT scores is available back to 1972, however, and a previous study identified a method for adjusting these scores to account for varying participation rates and demographics. The present paper aims to extend that earlier work, modifying it to facilitate meaningful trend analysis, using a substantially larger data set, relaxing its assumptions, and improving its approach to model selection and validation. The optimal model derived from that process is externally validated against both lagged 8th-grade and contemporaneous 12th-grade National Assessment of Education Progress (NAEP) scores, with good results.