Using recently released data from the Long-Term Trend Assessment of the National Assessment of Educational Progress, this study analyzed the mathematics performance of 9-year-old students between 1978 and 2004. The study goes beyond overall results by describing the assessment items and the change over time on each of those items. The data indicate that there have been substantial gains in ability to read and interpret tables and graphs and in calculating perimeter and area. Performance increased on most place-value and computation items, although performance on the majority of items involving measurement or money was relatively stable. The periods of greatest gain varied by item. As a general rule, however, improvement on items was greatest from 1986 to 1990 and again from 1999 to 2004--periods that had the largest gain on the assessment as a whole. (Contains 1 figure, 7 tables, and 10 notes.)