In this study it is investigated to what extent contextualized and non-contextualized mathematics test items have a differential impact on examinee effort. Mixture item response theory (IRT) models are applied to two subsets of items from a national assessment on mathematics in the second grade of the pre-vocational track in secondary education in Flanders. One subset focused on elementary arithmetic and consisted of non-contextualized items. Another subset of contextualized items focused on the application of arithmetic in authentic problem-solving situations. Results indicate that differential performance on the subsets is to a large extent due to test effort. The non-contextualized items appear to be much more susceptible to low examinee effort in low-stakes testing situations. However, subgroups of students can be found with regard to the extent to which they show low effort. One can distinguish a compliant, an underachieving, and a dropout group. Group membership is also linked to relevant background characteristics.