Some teachers cannot imagine using 3D printers in the classroom. Reasons given include lack of time or cost problems (Pielsticker & Witzke, 2017). For this reason, we would like to provide ideas and lesson plans that can be used directly by teachers.[br][br]Nowadays, it is important to use technology in schools to support and [b]motivate [/b]students in their learning. According to Witzke and Hoffart (2018), 3D printing is a great tool that can be used in schools in different ways. They mention three different ways to use it in schools. [br][list][*]First, there is a large amount of designed materials on the web that can be printed directly to be used in school. [/*][*]Secondly, teachers can develop individual materials especially for the students. [/*][*]Thirdly, students can model and print their own ideas, learning how to use CAD programmes. [/*][*]It also trains spatial imagination and self-directed learning can increase motivation.[/*][/list][br]There are many topics in the curricula that could be taught with the use of 3D printers. Already in preschool, children should get a first impression of mathematical thinking: Dealing with geometric figures and features, symmetry, ... Pupils in preschool mostly work with haptic materials to facilitate their understanding. These materials can easily be printed out. [br][br]Looking at the primary school curricula, one can see geometry as a big topic in all four grades. There is still an emphasis on playful approaches to mathematical concepts. Teachers can use GeoGebra applets to create small puzzles in which students can practice natural numbers between 1 and 9. Once created, they can be 3D printed. Games can also be invented to give pupils a first impression of what volume means. In the third and fourth grade curricula, there are two special sub-headings in the category of fields and figures. These are about shaping surfaces from other materials (toothpicks, matches, ...) and designing mosaics where 3D printing could be used as an added value[br][br]In the secondary school, the so-called "spiral principle" is very important. This principle means that there are the same topics in each school year, to which further aspects are added. The advantages of this principle are a manageable amount of new content and the repetition helps with memorisation. Teachers can use individually designed models for different topics. Visual and concrete objects provide an extra dimension to learning and help build more synapses. Hefendehl-Heber (2017) says that the origin of thinking is in acting and doing. This means that dealing with concrete materials in maths lessons promotes learning. Lengning, Meyer and Siebel (2014) have also compiled the advantages of using concrete materials in school. They say that students need them to develop appropriate conceptions of mathematical content. Furthermore, materials can help to practise, to reason and to switch between different modes of representation.[br][br]