A math teacher's memoir of twenty years in the classroom -- from West Springfield, Massachusetts to six schools across Iowa -- and the methods, mistakes, and students that changed how he thought about learning. During his first year teaching, Mark Vasicek watched experienced teachers retire and walk out the door with everything they had learned locked inside their heads. That bothered him from the start. This book is his attempt to leave something behind. He came to education at forty-five after twenty years as an engineer, bringing a constructivist's instinct for getting inside his students' thinking. In his final three years he discovered Peter Liljedahl's Building a Thinking Classroom -- and his teaching changed more in those three years than in the previous seventeen. It is not a math book, though the appendices contain the full geometry curriculum he built. It is a teacher's account of what the work actually costs and gives back. And at the end, it is a letter to his grandchildren -- a record of who he was for twenty years before they knew him.