The Ever-Changing NAEP Sample
The results of the latest National Assessment of Educational Progress long term trend tests (NAEP-LTT) were released last week. The data compare the reading and math scores of 9-, 13- and 17-year olds at various points since the early 1970s. This is an important way to monitor how these age cohorts’ performance changes over the long term.
Overall, there is ongoing improvement in scores among 9- and 13-year olds, in reading and especially math, though the trend is inconsistent and increases are somewhat slow in recent years. The scores for 17-year olds, in contrast, are relatively flat.
These data, of course, are cross-sectional – i.e., they don’t follow students over time, but rather compare children in the three age groups with their predecessors from previous years. This means that changes in average scores might be driven by differences, observable or unobservable, between cohorts. One of the simple graphs in this report, which doesn't present a single test score, illustrates that rather vividly.