Since the 1970s, the National Assessment of Educational Progress (NAEP) has monitored the academic performance of 9-, 13-, and 17-year-old students with what have become known as the long-term trend assessments. Four decades of results offer an extended view of student achievement in reading and mathematics. Results in this report are based on the most recent performance of more than 50,000 public and private school students who, by their participation, have contributed to our understanding of the nation's academic achievement. Both 9- and 13-year-olds scored higher in reading and mathematics in 2012 than students their age in the early 1970s (figure A). Scores were 8 to 25 points higher in 2012 than in the first assessment year. Seventeen-year-olds, however, did not show similar gains. Average reading and mathematics scores in 2012 for 17-year-olds were not significantly different from scores in the first assessment year. Closing achievement gaps is a goal of both national and state education policy. The results from the 2012 NAEP long-term trend assessments show some progress toward meeting that goal. Appended are: (1) Percentage of students assessed in NAEP reading, by age group and selected characteristics: Various years, 1971-2012; (2) Percentage of students assessed in NAEP mathematics, by age group and selected characteristics: Various years, 1978-2012; (3) Percentage of students identified as students with disabilities and/or English language learners excluded in NAEP reading and mathematics, as a percentage of all students, by subject and age group: Various years, 1990-2012; and (4) Percentage of 9-, 13-, and 17-year-old students with disabilities (SD) and/or English language learners (ELL) identified, excluded, and assessed in NAEP reading and mathematics, as a percentage of all students, by SD/ELL category: 2012. (Contains 38 figures and 10 tables.)