On math trails, students can make direct connections between real objects and mathematical ideas. In these extracurricular learning arrangements, which are in the form of a rally, students visit places and objects in the city or around the school to solve mathematical tasks. The tasks comprise measuring or estimating relevant sizes and quantities and placing them in a respective mathematical model. One indicator of the usefulness of math trails as a form of learning is the extent to which they entail modelling processes. In the present qualitative study, two 11th-grade school classes at Oslo, divided into five groups of three students each (N-groups=10), were individually recorded on video while working with math trails. Each group’s work was then analysed to determine observable modelling processes. The results for the groups in completing a math trail that involved circle calculation showed individual progressions between modelling phases while they worked on the tasks. The real objects were used in particular in various forms of data collection and validation. The article presents the study and reports on empirical findings on two groups of students’ modelling processes on math trails.