What does the "AI" in AIED buy?

Educational computing has spawned a number of fairly self contained intellectual communities. One is broadly covered by the phrase computer assisted instruction (CAI, CAL, CBT and its many variants) and the other by artificial intelligence in education (AIED, ITS, ICAI and its many variants). CAI is usually seen to be concerned to produce intelligently designed software to solve essentially educational goals by whatever computational means can be achieved. The methods are eclectic and the emphasis is on what really works from an educational point of view. AIED is traditionally seen as more of a research activity, as being concerned to produce programs of greater generality (though not necessarily of greater educational effectiveness) and as having its roots in cognitive psychology. In what particular ways do ICAI systems differ from CAI systems? The main answer lies in the way that an intelligent system can potentially tailor the interaction to suit the individual learner or group of learners. The paper briefly explores the question of how much educational difference the "AI" in an AIED system makes compared either to conventional classroom teaching or to conventional CAI methods. One criterion of educational effectiveness might be the amount of time it takes students to reach a particular level of achievement. Another might be an improvement in achievement levels, given the same time on task.