Can I just say from a practical point of view, primary classes are fairly static sort of places, you've got the teacher in the class all day, and if they say well let's have a micro in our classroom today that can be done, whereas a secondary teacher tends to wander round the school with a load of books under one arm and a bag of equipment under the other arm, and they've also got to carry a micro round or move a micro from one classroom to another — it's physically difficult, so in practice the primary teachers seem to find it easier to fit in with micros.