Book excerpt: This participant book, in combination with the facilitator's guide, forms a comprehensive professional development program designed to improve the efforts of site-based mathematics leadership teams for middle and high schools. Secondary Lenses on Learning prepares leaders to explore concepts in middle and high school algebra as a window into content, instruction, and assessment. You will learn how to assess the strengths and needs of your mathematics programs, set goals, and generate plans for ongoing improvement by engaging in extended explorations and conversations based on readings, problem-based activities, cases, and videos.