The following paper "Modelling in mathematics' class with specialization on Fermi-questions" deals with an upcoming new task type -- mathematical modelling. With the inauguration of the educational standards, modelling skills have recently attracted a great deal of attention. Hence, this paper discusses the progress of mathematical modelling and specializes on Fermi-questions. The relevance of mathematics has to be acknowledged in the classroom, particularly by establishing tight connections with the outside world. In the course of this paper, the significance of tasks close to reality comes to the fore, yet it exposes the different challenges they imply. Suggested ideas and solutions will be revealed to handle difficulties such as performance rating or inaccuracy while working on modelling tasks. Generally, this thesis gives teachers a first impression of mathematical modelling and supports them in dealing with modelling tasks in secondary school.