The modelling process carried out by 19 children aged 5-6 years in the context of a real problem is analysed to understand how temperature works and how it is measured. To carry out the analysis, the previously validated instrument "Rubric to Evaluate Mathematical Modeling Processes" (REM¬MOP) is used, which includes seven components related to the modeling cycle (understanding, structuring, mathematization, mathematical work, in¬terpretation, validation and presentation) and the corresponding indicators. The results show that, during this cycle: 1) children develop a first model to determine where the numbers are on the thermometer and how they are interpreted, based on the mathematical knowledge they mobilize; 2) they present important deficits especially in the last phases of the modeling cycle. It is concluded that it is necessary to promote the professional development of teachers to incorporate this type of activity from an early age.
Keywords: mathematical modelling, modelling cycle, assessment in math¬ematics, teaching practices, Early Childhood Education.