Although traditional textbooks may not guide students through explorations or encourage group work, as many standards-based curricula do, virtually all textbooks contain mathematically accurate information and problems that, with adjustment, can be leveraged to support mathematical curiosity, reasoning, and discussion. Teachers who recognize rich opportunities in their textbooks can develop routine curricular adaptations that turn parts of any curriculum into engaging learning experiences without too much extra work for the teacher. In this article, the authors draw from their experience in high school mathematics teaching, textbook design, curricular research, and teacher education to present curricular practices that take advantage of the worked examples, problem banks, "challenge" or "critical thinking" questions, and definitions in traditional textbooks. For each strategy, they illustrate how to adapt a section of a traditional textbook and explain how an updated version can offer students meaningful opportunities to reason and recognize rich mathematical connections. Their goal is to enable new high school mathematics teachers to continue developing their ability to nurture their students' reasoning and problem-solving skills.