XS-O is a low-cost interactive system that serves as a self-explanatory school computer. The machine dialog is easy to follow for the inexperienced user. The system includes a course on computer programming, a programming system for writing, editing, executing, and debugging programs interactively, and a filing system containing private and public libraries. The language offered to the user is a version of PASCAL. The system is realized on a small stand-alone computer which supports a small number of graphic terminals. (Author/DAG)