Work with PLATO, a computer-based teaching system which provides a means for individualizing instruction, is described. Children sit at terminals and respond to directives and questions on the screen by touching it or by typing a message. PLATO responds, and prescribes work in accordance with the child's previous performance. Curricular materials for teaching mathematics to pupils in grades 4-6 have been programmed, with strands on graphs, whole numbers, and fractions. How three children in one classroom interacted with PLATO is described and discussed. The vignettes try to portray the complexities of implementing PLATO mathematics in the classroom. The teacher's reactions to the use of PLATO are presented, along with excerpts from the logs she maintained for 2 years. An appendix lists the lessons available on PLATO. (MNS)