This study examines primary school students’ perception of functionality in their spontaneous programming language for controlling a simple robot. Classroom activities were designed in order to create opportunities for the students (year 1 and year 4) to discuss and develop together with their teachers a shared programming language for controlling a simple robot. The students spontaneously used (a) natural language, (b) images or (c) symbols when they created their programming language. The findings show that the students primarily perceived a code’s functionality as a question of readability, rather than how well it fit the purpose of controlling the robot. Possible consequences of the findings for teaching in technology education are discussed.