This article describes an intelligent computer-assisted language instruction system that is designed to teach principles of syntactic style to students of English. Unlike conventional style checkers, the system performs a complete syntactic analysis of its input, and takes the student's stylistic intent into account when providing a diagnosis. Named STASEL for Stylistic Treatment At the Sentence Level, the system is specifically developed for the teaching of style, and makes use of artificial intelligence techniques in natural language processing to analyze free-form input sentences interactively.