Lean Thinking is a methodology based on improving the efficiency of productive processes by removing non-value-added issues. This methodology was firstly applied in the manufacturing industry, but it has also been applied to many service companies, bringing very good results. In the last decade, some works have tried to research the adaptation of Lean principles and practices to teaching, especially in technology and other STEAM subjects. In this sense, the aim of this work is to deepen this new trend by establishing what issues are non-value-added (waste) ones in education and classifying these kinds of waste in order to be able to analyze how to eliminate them. For this purpose, we adapt the classification made in other kinds of processes and extend other authors' findings regarding this topic.