Hemodynamic measures of brain activity can be used to interpret a student's mental state when they are interacting with an intelligent tutoring system. Functional magnetic resonance imaging (fMRI) data were collected while students worked with a tutoring system that taught an algebra isomorph. A cognitive model predicted the distribution of solution times from measures of problem complexity. Separately, a linear discriminant analysis used fMRI data to predict whether or not students were engaged in problem solving. A hidden Markov algorithm merged these two sources of information to predict the mental states of students during problem-solving episodes. The algorithm was trained on data from 1 day of interaction and tested with data from a later day. In terms of predicting what state a student was in during a 2-s period, the algorithm achieved 87% accuracy on the training data and 83% accuracy on the test data. The results illustrate the importance of integrating the bottom-up information from imaging data with the top-down information from a cognitive model.T his article reports a study of the potential of using neural imaging to facilitate student modeling in intelligent tutoring systems, which have proven to be effective in improving mathematical problem solving (1, 2). The basic mode of operation of these systems is to track students as they solve problems and offer instruction based on this tracking. These tutors individualize instruction by two processes, called "model tracing" and "knowledge tracing." Model tracing uses a model of students' problem solving to interpret their actions. It tries to diagnose the student's intentions by finding a path of cognitive actions that match the observed behavior of the student. Given such a match, the tutoring system is able to provide real-time instruction individualized to where that student is in the problem. The second process, knowledge tracing, attempts to infer a student's level of mastery of targeted skills and selects new problems and instruction suited to that student's knowledge state. Although the principle of individualizing instruction to a particular student holds great promise, the practice is limited by the ability to diagnose what the student is thinking. The only information available to a typical tutoring system comes from the actions that students take in the computer interface. Inferences based on such impoverished data are tenuous at best, and brain imaging data might provide a useful augmentation. Recent research has reported a variety of successes in using brain imaging to identify what a person is thinking about (e.g., refs. 3-6) and identifying when mental states happen (e.g., refs. 7-9).Although the methods described here could extend to knowledge tracing, this article will focus on model tracing where the goal is to identify the student's current mental state. Two features of the intelligent tutoring situation shaped our approach to the problem: (i) Given that instruction must be made available in real time, inferences about mental state ca...