The Mayonnaise model of teaching
Most of us buy our mayonnaise in jars from the supermarket (so do I, actually, apart from special occasions: and even then I have a jar in reserve in case my own efforts go horribly wrong). I have a friend who always used to make his own and proclaimed that it was almost impossible to get it to curdle: it was some time before he realised that his home-made version was always curdled, and he just did not know what the real thing should look like. There's a moral in that somewhere, but not the one we are about to draw.
Click here for a slightly more authoritative guideThe basic process of making mayonnaise is to put the egg-yolks and a few other optional ingredients in a bowl, and to beat them (manually) as hard as you can while adding the oil ever so gradually, drop by drop by drop. As the yolks and the oil become amalgamated into an emulsion, it is possible to speed up the rate at which the oil is added, but do it too fast and it will curdle. Do it too slowly, of course, and your arm will fall off before you get to eat it.
What has this got to do with learning and teaching?
Creating a stable emulsion involves in this case the introduction of new material to be combined with what is already there. Unless the original material (the yolks plus whatever oil has been amalgamated) is somehow destabilised (beaten), it cannot incorporate (assimilate or accommodate) the new stuff (oil). Adding the oil requires patience and a constant attention to the state of the emulsion so far: going too fast will result in overload and the separation of the elements. (In the case of mayonnaise, a curdled product necessitates starting again adding the curdled mess to fresh yolks — it is not wise to push the analogy that far). You can tell the state of the emulsion by its shiny look.
So it is a matter of being able to tell how much new stuff to feed in, and when. When are the students ready? And if you stop beating them (metaphorically, of course), can they take any more? The analogy also breaks down at another level — the teacher is not just adding oil. Students are ready for different amounts of different ingredients at different stages.
This model can be applied at the level of curriculum planning, but it seems to me to make most sense at the second-to-second level of the face-to-face teaching session.
Of course, as anyone who has made mayonnaise will tell you, as you incorporate more oil, the emulsion gets thicker — it is probably best not to dwell on that, either!