 It is therefore not surprising that tutorial dialogue systems are closer to commercial practicality, with demonstrated learning benefits relative to conventional instruction in various evaluations, than collaborative problem solving systems for realistic applications. Tutorial dialogue systems have been built for numerous domains and potential clienteles, ranging from K-12 subjects to computer literacy and novice programming, qualitative and quantitative physics, circuit analysis, operation of machinery, cardiovascular physiology, fire damage control on ships, negotiation skills, and more (e.g., see Boyer et al. 2009; Pon-Barry et al. 2006). Among the most successful tutorial systems are reading tutors (e.g., Mostow and Beck 2007; Cole et al. 2007), since the materials presented to the learner (in a “scaffolded” manner) are relatively straightforward to design in this case, and the responses of the learner, especially when they consist primarily of reading presented text aloud, are relatively easy to evaluate. For the more ambitious goal of fostering reading comprehension, the central problem is to design dialogues so as to make the learner's contributions predictable, while also making the interaction educationally effective (e.g., Aist and Mostow 2009).