The study evaluated usability of the "Opón-Ìmo" Technology Enhanced Learning System ("OTELS"), an educational software deployed for teaching and learning across state-owned senior secondary schools in Osun State, Nigeria. It employed a descriptive research design of the survey type. Eight teacher-educators in Educational Technology and Computer science were purposively selected from four public higher institutions in the state to critically evaluate how usable the software is. A researcher self-designed instrument, tagged the E-learning Usability Evaluation Questionnaire for Teacher-educators (EUEQT), was used for data collection. Reliability of the instrument was ascertained using Pearson Product Moment Correlation. The instrument yielded a reliability coefficient of 0.73 which indicated its suitability for the study. Findings from the study revealed that "OTELS" did not conform to most of the guidelines generated to evaluate the software (heuristics guidelines); only six out of fifteen did so. Respondents' area of specialisation was also found not to have an influence on the evaluation of the software. Based on its findings, the study therefore recommends a review of the educational software in order to increase its suitability for teaching and learning purposes.