Using an interactive computer system called NEWBASIC/CATALYST, both students and teachers can act as authors of programs. NEWBASIC/CATALYST incorporates an implementation of BASIC, system-level interactive features, and a general capability for extension through use-oriented function attachment. Interacting at the system level, students can mix the advantages of independent or "solo" mode computing with those of guided or "dual" mode interaction. Illustrations of this are given. Preliminary experience with the system was in an urban secondary school setting. (Author/MF)