The Nation's Report Card[TM] informs the public about the academic achievement of elementary and secondary students in the United States. Report cards communicate the findings of the National Assessment of Educational Progress (NAEP), a continuing and nationally representative measure of achievement in various subjects over time. Since 1969, NAEP assessments have been conducted periodically in reading, mathematics, science, writing, U.S. history, civics, geography, and other subjects. NAEP collects and reports information on student performance at the national and state levels, making the assessment an integral part of the nation's evaluation of the condition and progress of education. This report presents results for student performance on the systematic measure of vocabulary included in the 2009 and 2011 NAEP reading assessments. While previous NAEP assessments had included some vocabulary questions, the new framework for the 2009 assessment provided criteria for developing vocabulary questions as well as prescribing the number of questions to be included in each comprehension section of the assessment. This systematic assessment of vocabulary allows for NAEP to more fully assess the impact of vocabulary knowledge on students' comprehension and makes it possible to report on students' vocabulary performance. Vocabulary results from the 2009 reading assessment are based on nationally representative samples of 116,600 fourth-graders, 103,400 eighth-graders, and 44,500 twelfth-graders. Results from the 2011 assessment are based on samples of 213,100 students at grade 4 and 168,200 students at grade 8. The reading assessment was not administered at grade 12 in 2011. NAEP vocabulary results are available for 2009 and 2011 at grades 4 and 8. As grade 12 was not assessed in 2011, results for twelfth-grade students are available for 2009 only. The overall average vocabulary scores for fourth- and eighth-grade students in 2011 were not significantly different from 2009, but there were some changes in the scores for students performing at selected percentiles on the vocabulary scale. At grade 4, scores were lower in 2011 than in 2009 for higher-performing students at the 75th and 90th percentiles. At grade 8, lower-performing students at the 10th percentile scored higher in 2011 than in 2009. Eighth-graders at the 75th and 90th percentiles scored lower in 2011 than in 2009. (Contains 4 figures and 6 tables.)