The Strengthening of Mathematics and Sciences in Secondary Education (SMASSE) in-service training programme was set up in 1998 as an intervention measure following the declining quality of teaching and learning in Mathematics and Sciences in Kenya. SMASSE''s strategy was a pedagogical shift coined as the Activity-focused, Student- Centered, Experimenting and Improvisation (ASEI) through Plan, Do, See and Improve (PDSI) approach. This innovation has a Constructivists'' approach of teaching and learning. The purpose of the study was to evaluate the extent to which the SMASSE in-service training had enhanced the capability of the Biology teachers to improve the performance in Biology in Kajiado District, Kenya. The study used an evaluation research design to determine; the use of the ASEl/PDSI classroom practice by teachers, the participation of students in the class room, the management and administration of resources by the principals and the attitude of the students and teachers towards the learning and teaching of Biology. Six out of 22 schools formed the sample. Questionnaires and an Observation schedule for facilities were used to collect data.