Who writes the NCLB standardized tests?

There's no single entity that writes the standardized tests used under the No Child Left Behind Act (NCLB). NCLB didn't mandate specific tests from a single provider. Instead, it required states to develop and administer their own standardized tests, often choosing from a variety of commercially available tests from different publishers. These publishers included (and still include) companies like Pearson, McGraw-Hill, and others. The specifics varied greatly by state.