Plus-Minus Trainer is a learning software enabling children practicing additions and subtractions on a device running Android. Multiple training modes are provided for this cause: + Online mode: Exercise written addition and subtraction. Tasks and Solutions are retrieved and respectively saved from a web server, located at https://schule.learninglab.tugraz.at/plusminus/. Following modes do not need internet access. The difficulty of the randomly generated tasks can be changed in the application's settings. + Plus-Minus mode: Solving of randomly generated written additions or subtractions. + Speed mode: Solving of randomly generated calculations within a timebox of 60 seconds including a high score list. + Tree mode: Solving of three randomly generated Calculations connected by a calculation tree. + Analogy mode: Solving of similar tasks (e.g. 5+2 and 2+5) + Symbolic addition: Solving of simple inline additions with auxiliary symbols. + Symbolic subtraction: Solving of simple inline subtractions with auxiliary symbols.