Mark Twain School, also known as the Poplar Bluff Museum, is a historic school building located at Poplar Bluff, Butler County, Missouri. It was built in 1910, and is a two-story, "H"-plan, Classical Revival style brick building. The building consists of two, parallel, rectangular-plan, hipped roof blocks joined by an enclosed two-story flat roof corridor. It remained in use as an elementary school until 1988. It was listed on the National Register of Historic Places in 1998.