This paper proposes a qualitative systems dynamics model that explains how students' work placement experiences either enhance or hinder the growth of their occupational competency and self-efficacy. The model is developed from qualitative analysis of work placement experiences of mechanical engineering students from a South African university of technology. Findings from the analysis show that students' occupational competency and self-efficacy could be considered emergent outcomes of interactions of the learning environment, mentor posture, mentor capacity, mentor availability, meaningfulness of work, scope of work, agency, doing work, co-participating, participation trajectory and performance trajectory. The explanation of the factors and social mechanisms that influence students' occupational competency and self-efficacy that is offered by the qualitative systems dynamics model would enable the implementation of work placement programs in a manner that would promote rather than hinder the growth of these two indicators of student employability.