A widely used instrument was implemented to ascertain the mathematical modelling competency displayed by a cohort of South African learners in grade 10 and grade 12 of the school mathematics programme in South Africa. The cohort comprised 471 grade 10 and 200 grade 12 learners from schools serving learners from low socio-economic status communities. A quantitative survey design was used to investigate whether there are differences between the mathematical modelling competencies of the two cohorts. Differences along gender lines were also investigated, as were linkages between mathematics achievement levels and the displayed mathematical modelling competency. Lastly, differences between the mathematical modelling competencies between the groups were pursued. Non-parametric statistical procedures were used to analyse the data. The results show that although the mathematical modelling competency was low for both groups there were significant differences for the overall modelling competency. For three of the competencies, there were significant differences between the groups but not all in favour of the grade 12 group. The results are finally discussed in relation to the structuring effect the curriculum document, textbooks and high-stakes examinations have on the realization of the espoused inclusion of mathematical modelling in the curriculum.