ACT requested assistance from the National Center for the Improvement of Educational Assessment (Center for Assessment) to investigate declines of scores for states administering the ACT to its 11th grade students in 2018. This request emerged from conversations among state leaders, the Center for Assessment, and ACT in trying to understand the 2018 score declines, particularly in census testing states. The primary goals of the Center's investigation were to: (1) identify possible explanations for the observed score declines based on information provided by ACT; (2) make recommendations to ACT and states for additional analyses to confirm or uncover explanations for the observed trends; and (3) suggest changes to ACT's existing processes or procedures that can help expedite the detection of such trends or mitigate potential sources of error in the future. The Center pursued three general lines of inquiry to understand potential contributions to the ACT score declines in 2018. This report examines: (1) ACT's established procedures; (2) implementation of its established procedures; and (3) select contextual factors related to the test-taking populations.