Do you need a way to practice writing thesis statements with your AP US History students? This worksheet covers both content and writing skills! After a brief review of what a thesis SHOULD be (DADS--defensible, analytical, debatable, and specific), students are given several statements to evaluate and correct. Then they practice writing their own thesis through a guided look at a causation question about development of the late 19th century frontier. Use in class in place of lecture, or assign as homework to reinforce material that you've covered: either way your students are getting great writing practice!