<p>This study investigated the predictors of simulation integration in physics instruction among in-service secondary school teachers in Nigeria, using an integrated theoretical framework that combined the Technology Acceptance Model and the Will-Skill-Tool model. A convergent parallel mixed methods design was employed. Quantitative data were collected from 375 physics teachers using a validated instrument, the Physics Teachers Simulation Integration Questionnaire, and analysed through confirmatory factor analysis and structural equation modelling. Qualitative data were gathered through semi-structured interviews with six teachers to explore contextual barriers, supports, and professional learning needs. The model examined the influence of attitudes, beliefs about ICT, ICT competency, institutional support, resource availability, and self-efficacy on simulation integration. Contrary to theoretical expectations, none of the hypothesized direct, mediated, or moderated paths were statistically significant, and model fit indices indicated poor structural alignment. Thematic analysis of interview data revealed systemic constraints which included infrastructural deficits, weak leadership support, and limited professional development that helped explain the null quantitative findings. These results suggest that individual teacher readiness is insufficient for simulation integration in under-resourced contexts. The study calls for an expanded ICT adoption framework that incorporates school leadership, policy enactment, and institutional culture. Implications are discussed for teacher professional development, ICT policy, and future research on technology integration in sub-Saharan Africa.</p>