The general performance in mathematics in Kenya has been declining over the past years. This prompted the researchers to investigate the influence of Strengthening Mathematics and Science in Secondary Education (SMASSE) In Service Education and Training (INSET) on students' attitudes towards mathematics performance in public secondary schools of Rangwe division. The objectives of the study were to investigate whether SMASSE-INSET had changed the students' attitudes towards mathematics performance and whether there were any significant differences in students' attitudes based on school categories. The study was conducted in Homa Bay Sub County, Rangwe division using a descriptive survey design. The respondents of the study were selected from the Form three students of the year 2013. A sample of 203 students was obtained from the boys' school, the girls' school and mixed day schools using stratified random sampling technique. Content analysis was used to obtain the data on students' performance from 2004 to 2012. Data was collected through the use of students' questionnaire and analysis done using both descriptive and inferential statistics. The study established that the students' attitude towards mathematics was positive though the positive attitude had not been translated to improved performance in mathematics.