This idea is totally stolen from a former colleague of mine, Andrew Dales.
His question: what happens after an intervention? Specifically, he framed the question perfectly as the following graph:
So, assuming that the intervention produces a greater increase in attainment than control (which I’ve exaggerated significantly for the purposes of clarity), what happens afterwards?
Does the intervention instil in pupils some newfound ability to continue progressing at a greater rate than they would have before (route A)?
Do the pupils return to the same rate of progress as before the intervention, staying ahead of where they were before (route B)?
Or do they, post-intervention, progress at a lower rate for some time, returning to their original path (route C)?
Of course, this will depend on the intervention. As teachers, I feel that we should consider which approaches will help our pupils to follow route A (or at least B!), not just those which produce the largest improvement over the time span of the intervention.
In the same way as Daniel Kahneman introduces new terminology in Thinking, Fast and Slow, I think it could be valuable to introduce the new terminology into educational research: “Is this a Route A intervention, or will the students revert to control via Route C?”
I wonder how much research tries to answer this question? My suspicion is not a lot.