This chapter describes theoretical issues, basic research, and computational methodology underlying local student modeling in TAPS, an ITS for improving word-problem skills at grade-levels 4 through remedial 13. By local student modeling we refer to system capabilities that carry out on-line performance monitoring and error recognition for the purpose of informing local tutoring decisions, and distinguish these from system capabilities that focus on global evaluations of student progress for the purpose of selecting and sequencing curriculum-level instructional goals.