CONCLUSION
The study concluded that teachers’ age, gender, professional qualifications and professional experience did not have significant effect on academic achievement in secondary schools in Nyandarua County. However, teachers’ job group and workload significantly affected academic achievement. The study also concluded that the frequency of issuing assignments, teachers ensuring that students completed assignments and timely marking of the assignments significantly affected academic achievement. Further, teachers evaluating students’ CATs results and providing individualized learner attention to weak students have an impact on academic achievement. Timely completion of Form Four syllabus and setting performance targets for KCSE performance were also statistically significant in predicting academic achievement. Teacher background characteristics and classroom instructional practices therefore do make a difference in students’ academic achievement.