This study examined secondary school teachers' beliefs about the purpose, importance, and principles of assessment. Forty-seven Literature-in-English teachers in the Ibadan metropolis, Nigeria, were sampled using the mixed-method research design. Literature-in-English Teachers' Assessment Beliefs Questionnaire (r = 0.76) and Literature-in-English Students' Class-Assessment Checklist were used in collecting quantitative data. Ten teachers were interviewed. Analyses of data suggest that teachers considered assessment an essential element of teaching, but they could not translate their beliefs into practice. Possible causes of the inconsistencies were not established, suggesting areas for future research. Some recommendations were made.