Marble tracks are a very popular toy and big ones can be found in science centres in many countries. If children want to make a marble track themselves it is quite a job. It takes a long time, they can take up a lot of space and most structures are quite fragile, as the materials used can very quickly prove unfit for the task and do not last very long. Not least, it is difficult to make a good working track. Obviously science, technology, engineering and maths (STEM) skills, such as trial and error, practice, evaluation and redefining, are all involved in this, but there is very little chance that teachers will let their pupils make marble runs in the classroom and keep them there for weeks. Could a class of 30 children, working in pairs or even on their own, build their own marble tracks during a 2-3 week period? The author took up the challenge with his class. In this article, the author presents how build marble tracks and how it is possible to have 20 or more marble tracks running for several weeks in the classroom.