 When the Reading Tutor notices a student misread a word, skip a word, get stuck, hesitate, or click for help, it responds with assistance modeled in part on expert reading teachers, adapted to the capabilities and limitations of technology.The Reading Tutor dynamically updates its estimate of a student’s reading level and picks stories a bit harder (or easier) according to the estimated level; this approach allows the Reading Tutor to aim for the zone of proximal development, that is, to expand the span of what a learner currently can do without help, toward what he or she can do with help.The Tutor also scaffolds (provides support for) key processes in reading.