The strange case of the disappearing NAEP (Tom Loveless, Brookings)

The long term trend test of the National Assessment of Educational Progress (LTT NAEP) is the longest running test of student achievement that provides a scientifically valid estimate of what American students have learned. For over four decades, beginning with a science assessment in 1969, the LTT NAEP has tested randomly-selected groups of students age 9, 13, and 17 in several school subjects. Reading and mathematics have been assessed the most. The reading test began in 1971 and the math test in 1973.[i]

https://www.brookings.edu/blog/brown-center-chalkboard/2016/10/17/the-strange-case-of-the-disappearing-naep/