In this mixed methods study, qualitative, quantitative, and single-case methods were combined to provide a comprehensive investigation of teacher and student outcomes following practice-based professional development (PBPD) for self-regulated strategy development (SRSD) in writing. Qualitative observations were used to determine outcomes among the three-fourth grade teachers involved, a nested quantitative model was used to analyze classwide student writing outcomes across 53 students in the three classes, and single case design was used to determine differential outcomes among randomly selected struggling and average writers in each class. PBPD was followed by coaching for differentiation based on student performance and fidelity as teachers taught their students strategies for writing timed imaginary stories (with self as main character), as required by the state writing test. Qualitative results indicated two teachers did not differentiate writing instruction without coaching; one teacher was unresponsive to coaching and did not differentiate instruction. Classwide analysis demonstrated significant growth in writing at the class level for students from baseline to posttesting. Single case design results indicated mixed outcomes among struggling and average writers and instances where instruction was not effective. Teachers indicated high social validity for PBPD and for SRSD; students indicated high social validity for SRSD. Results across the multiple methods illuminate growth and struggles often disguised in group data and are addressed to aid in understanding and enhancing PBPD as well as instruction in SRSD and other evidence-based practices. Limitations and future research directions are discussed.