AbstractWithin the purview of educational settings, students possess some unique traits which make them react in an unexpected manner to the learning environment. Students are not only unique in terms of personality characteristics, family background, age and gender, they also showed diverse states of mind and enthusiastic reactions to the environment. Therefore, this study modelled the Big Five personality traits and academic achievement of students in Lagos State, Nigeria. A non-experimental design of scale development research type was adopted. A sample of 480 senior secondary school III students selected through multi-stage sampling procedure across the education districts 2 of Lagos State. Student’s Personality Traits Scale (SPTS) and Physics Achievement Test (PAT) were deployed to capture the needed data after subjecting them to exploratory factor analysis using the psych package implemented in R programming language and item calibration of Item Response Theory. Data were analysed usin.....