I found "All cohorts learn equally," as intuitively plausible as "people of different heights grow at the same rate".
I think this is an important point of this study because one possible criticism of MOOCs is that they might only work for people who are already very high functioning and good at figuring stuff out themselves, and people who are more apt to struggle might be left completely in the dust (more so than in a live-contact situation). So the fact that this was not true is interesting.
Two questions arise:
(1) To what extent is this true?
For example a first year undergraduate physics course won't teach much to average 3 year olds or to physics Nobel prize winners. There's a limit to the range of audience that can effectively be reached.
(2) To what extent does this even need to be true?
As has always been true, you can have different classes for different levels of ability, preparation, and so on. There's no need to even attempt to make one size fit all, as that will inevitably lead to detrimental compromises. You just need one size to fit a reasonable range. With a menu of courses (MOOCs or otherwise) you just want people to be able to select what fits them.
