Engineers commonly use rules, theories and models that lack scientific justification. Examples include rules of thumb based on experience, but also models based on obsolete science or folk theories. Centrifugal forces, heat and cold as substances, and sucking vacuum all belong to the latter group. These models contradict scientific knowledge, but are useful for prediction in limited contexts and they are used for this when convenient. Engineers' work is a common prototype for the pupils' work with product development and systematic problem solving during technology lessons. Therefore pupils should be allowed to use the engineers' non-scientific models as well as scientific ones when doing design work in school technology. The acceptance of the non-scientific models for action guidance could be experienced as contradictory by pupils and teachers alike: a model that is allowed, or even encouraged in technology class is considered wrong when doing science. To account for this, different epistemological frameworks must be used in science and technology. Technology is first and foremost what leads to useful results, not about finding the truth or generally applicable laws. This could cause pedagogical problems, but also provide useful examples to explain the limitations of models, the relation between model and reality, and the differences between science and technology.