Inventions Bring Change explains how four different inventions, the reaper, the railroad, water-powered mills, and the cotton gin changed the course of American history. While each of the four books focuses on a different invention, its history, and its impact on society, the same key concepts are developed across books to help students focus on the big ideas. The theme explores how inventions have caused changes in people's daily lives by making work easier and more efficient and how inventions impact the development of new inventions. Students use the specific content and vocabulary within each book to discuss and examine these big ideas, or Key Concepts. The Theme Set Program is designed for differentiated instruction. Each Theme includes four books written at four different reading levels.