This study investigated the extent to which teachers’ learning of Technological Pedagogical Content Knowledge (TPACK) has an impact on their technology use and classroom practices. The study involved 12 in-service teachers and 40 students from Kibasila secondary school in Tanzania. During the study, teachers participated in training about TPACK and in teacher design teams they designed technology-enhanced Biology, Chemistry and Physics lessons. Data were collected through a teacher questionnaire, an observation checklist, student questionnaire and a teacher interview. Results showed that after learning TPACK, teachers’ classroom practices shifted from teacher-centered approach to learner-centered approaches that utilize technology. Students' interest on the lessons was also enhanced. In addition, there was an increase in the interaction between students and teachers during the classroom session. Given these findings, we concluded that, teachers’ development of TPACK has an impact on the teachers' teaching approaches.