Although the American School Counselor Association National Model reflects the importance of high-quality school counseling core curriculum, or classroom guidance, as part of a comprehensive school counseling program, school counselors are often challenged by the complexities of designing an effective classroom guidance curriculum. This conceptual paper addresses these challenges by proposing the use of "Understanding by Design," a research-based approach to curriculum design used widely in K-12 classrooms across the United States and internationally, to strengthen classroom guidance planning. We offer principles for developing a classroom guidance curriculum that yields more meaningful and powerful lessons, makes instruction more cohesive, and focuses on what is critical for student success.