Constraint-based modelling (CBM) was proposed in 1992 as a way of overcoming the intractable nature of student modelling. Originally, Ohlsson viewed CBM as an approach to developing short-term student models. In this talk, I will illustrate how we have extended CBM to support both short- and long-term models, and developed methodology for using such models to make various pedagogical decisions. In particular, I will present several successful constraint-based tutors built for a various procedural and non-procedural domains. I will illustrate how constraint-based modelling supports learning and meta- cognitive skills, and present current project within the Intelligent Computer Tutoring Group.