A founding ideal of American democracy is that merit, not accident of birth, should determine individuals' income and social status. Schools have assumed a major role in judging key elements of merit among young people--namely, academic skills, hard work, self-discipline, and cooperative behavior. Schools do so mainly by evaluating students in a variety of subjects deemed important for success later in life. No one expects outcomes at the end of the schooling process to be the same for every student, since initial ability varies, and some young people are more disciplined and willing to work harder in school than others. Yet, when students' inherent characteristics--such as race, gender, or parents' economic and social capital--rather than their innate ability, hard work, and discipline systematically affect their school outcomes, this threatens democratic ideals. Analysts have studied persistent gaps in U.S. student achievement--particularly between blacks and whites, Hispanics and whites, and different social-class groups--for many decades. They have also examined achievement gaps between boys and girls. Considerable evidence exists that race continues to be an important factor in explaining achievement differences, however, social-class differences account for much of the black-white and Hispanic-white achievement gap. Disadvantaged minority children, such as African-Americans and Hispanics, are much more likely to be poor than are white children. Furthermore, there are new questions about whether race and social class interact with gender, resulting in a particularly deleterious effect on the academic performance of disadvantaged minority boys, and whether school conditions have a greater effect on boys or girls. The good news in the literature is that achievement differences between blacks and whites and between Hispanics and whites have apparently declined over time. The bad news is that until recently the achievement gap between higher and lower-social class groups appeared to be increasing, particularly between the children in the highest-income group and everyone else. This paper advances the discussion of these issues by analyzing trends in how race/ethnicity, social class, and gender relate to academic performance in U.S. schools. The focus is on different grades and different subjects (mathematics and reading) over the past 10 years and on mathematics since the mid-1990s. Changing achievement gaps between students of different race/ethnic identification, gender, social class, and English language-ability designation in the fourth and eighth grades over the past decade and a half, and how sensitive these gaps are to school composition in terms of the proportion of poor or minority peers were analyzed. Many of those achievement gaps develop well before entry into school and, on average, continue--or get larger as students progress in school (because those who start out behind academically are more likely to attend schools with fewer resources, which may compound, instead of compensate for, initial disadvantages). Lower-income families are also less able and less likely to invest in academically enriching activities for their children outside of school. Student micro data from the National Assessment of Educational Progress (NAEP) were used to estimate the math and reading performance of students in fourth and eighth grade from 2003 to 2013, as well as students' performance in eighth-grade mathematics only from 1996 to 2013. This report makes the argument that changes of patterns of change, or lack of change in patterns have important implications for what is happening in U.S. schools and American society.