This chapter investigates in what ways school technology may reflect professional technological practices. Using the historical development within the aeronautical industry as an example, characteristics of technological practice and knowledge are presented. In particular, it is referred how manufacturing, testing, and operating a technological device produce knowledge that affects the design process and the fundamental design concepts of the artefact. By means of a literature review and a multi-case study, it is found that D&T classrooms may have similarities with how design and engineering takes place in a professional community. The role of heuristics and repetitive testing is important for both cases. Examples from both professional engineering and classroom activity show that utilizing science and mathematics in a fruitful way in developing technology is challenging. However, there are some distinct differences as well. The students´ lack of expertise is an imperative for D&T teachers to provide students with basic understanding of the fundamental design concepts involved in the activity.