This paper describes VP2, a system that has been implemented to tutor nonnative speakers in English. This system differs from many tutoring systems by employing an explicit grammar of its user's native language. This grammar enables VP2to customize its responses by addressing problems due to interference of the native language. The system focuses on the acquisition of English verb‐particle and verb‐prepositional phrase constructions. Its correction strategy is based upon comparison of the native language grammar with an English grammar. VP2is a modular system: its grammar of a user's native language can easily be replaced by a grammar of another language. The problems and solutions presented in this paper are related to the more general question of how modelling previous knowledge facilitates instruction in a new sk