The purpose of this study is to provide knowledge about the impact of using one-to-one computers in educational practice, which in this case is language development in a multilingual classroom. The questions investigated are if and how the pupils’ learning is promoted and how the teacher’s instruction is influenced when each pupil has access to a personal computer. A 4th grade class, where all pupils speak Swedish as a second language, has been observed. Analyses are carried out by Activity Theory (AT). Language development and learning is in focus, as well as socio-cultural theories of mental tools. Having one-to-one computers in the studied classroom practice indicates that the computer is the actual mediating artifact in the students’ language development. The teacher becomes invisible and acts as technical support. The computer with its spellcheck function has taken over the teaching role. The interaction among the classroom actors appears as minor