In this qualitative research case study, multi-site cases of teachers'' practices and experiences about chemistry unit lesson planning and implementation following an in-service teacher education program in Kenya are examined. Specifically, a descriptive comparison of chemistry educators in the Strengthening of Mathematics and Science in Secondary Education (SMASSE) In-service Program in four different school settings (boys'' boarding, girls'' boarding, mixed boarding, and mixed day) was made. The intent of this study was to determine what changes, if any, teachers made in the design and implementation of their lessons, how these changes were implemented, and why the teachers made such changes. Among other findings, the study established that participants planned, prepared and implemented student-centered activity lessons using a new lesson plan format during chemistry unit lessons on the Periodic Table, "Mole Concept", Electrochemistry, and Organic Chemistry. They improvised teaching/learning materials, where conventional equipment were not available in school.