Children in a first-grade class who were taking their first steps in formal mathematical knowledge were given a sequence of five modelling tasks during their regular mathematics lessons. These tasks were different in nature from the problems they encountered in their textbooks. They are more complex and challenging, requiring analysis of the problem situation and decisions about the mathematics that could be used. The nature and implementation of the tasks involved new curricular goals and new problem solving norms aimed at developing children's modelling competencies. The findings show that the children were able to accept the new norms that promoted situation analysis and realistic considerations. They increased their use of argumentation, utilised existing additive strategies and displayed some use of multiplicative structures which the children had not encountered formally yet.