Research has identified a number of problems limiting the implementation of content standards in the classroom. Curriculum materials may be among the most important influences on teachers' instruction. As new standards roll out, there is skepticism about the alignment of "Common Core--aligned" curriculum materials to the standards. This analysis is the first to investigate claims of alignment in the context of fourth-grade mathematics using the only widely used alignment tool capable of estimating the alignment of curriculum materials with the standards. The results indicate substantial areas of misalignment; in particular, the textbooks studied systematically overemphasize procedures and memorization relative to the standards, among other weaknesses. The findings challenge publishers' alignment claims and motivate further research on curriculum alignment.