Examinations can be messy when used summatively to gauge the level of attainment posing adverse influence to the process of curriculum implementation. This influence is likely to hit hard various teachers’ practices such as lesson preparation, lesson implementation, classroom management, formative assessment and syllabus completion. The purpose of this study was to investigate the perceptions on summative evaluation, both classroom summative evaluation done at the end of the term/year and the national examination, and its influences on the teachers’ classroom practices in Rarieda Sub-county, Siaya County, Kenya. The study was guided by motivational theory-extrinsic and intrinsic theories. This study employed descriptive and correlational research designs. Stratified sampling and cluster sampling techniques were used to obtain the desired sample of 250 teachers. Questionnaire and focus group discussion were used to gather information from the respondents. The questionnaires’ construct, content and face validity was ascertained through expert judgments and the reliability was established through pilot testing yielding Cronbach’s alpha coefficients of .620 and higher. The data was analyzed using frequencies, percentages, means, standard deviations, and Pearson product-moment correlation coefficient. The study revealed that there is significant relationship between perceptions on classroom summative evaluation and classroom management (r=.264), formative assessment (r=.383) and syllabus completion (r=.192) and between perceptions on national examination and lesson preparation (r=.281), lesson implementation (lower-order/higher-order) (r=.183), (r=.281), classroom management (r=.451), and formative assessment (r=.541). The study recommended that teachers should give their focus to acquisition of attitudes, values and skills that are needful in this century and adopt good classroom practices to ensure in-depth learning.