Educational inequality due to family socioeconomic status (SES) has been the focus of both public dialogue and education research in the United States for many years. The current study aims to understand how educational inequality due to family SES has changed in the United States. Specifically, the study focuses on the changes in achievement gaps between high and low SES students between 2003 and 2017 and the changes in the performance of low-SES students over time. Data from the National Assessment of Educational Progress (NAEP) grade 8 mathematics assessment were used for the analyses. Results show that the SES achievement gap at the national level has remained the same over time. State-level results suggest that 34 of the 50 states' SES achievement gaps experienced no significant change between 2003 and 2017, 14 gaps widened, and only two SES gaps narrowed. In addition, at the national level, more low-SES students achieved at the NAEP Basic and at the NAEP Proficient levels over time with a majority of states improving their low-SES students' performance. In conclusion, the study contributes to the existing literature not only by reflecting on U.S. national trends using an effective SES index, but also by providing state-level results. It also collects trend data on states' macro-level indicators, including economic growth, social inequality, and educational expenditures, allowing state-specific findings to be presented in the context of changes in macro-level context. Initial explorations of relationships between state SES achievement gap trends and macroeconomic factors are presented to motivate future research. The trends in SES achievement gaps and the specific policy contexts are presented in greater detail for 13 states/jurisdictions.