It was probably mentioned in the earlier discussions, but I believe the "two humps" pattern can easily be explained by bad teaching. If it hapens in the whole profession, maybe no one has yet discovered a good way to teach it, because most of the people who understand the topic were autodidacts.

As a model, imagine that a programming ability is a number. You come to school with some value between 0 and 10. A teacher can give you +20 bonus. Problem is, the teacher cannot explain the most simple stuff which you need to get to level 5; maybe because it is so obvious to the teacher that they can't understand how specifically someone else would not already understand it. So the kids with starting values between 0 and 4 can't follow the lessons and don't learn anything, while the kids with starting values 5 to 10 get the +20 bonus. At the end, you get the "two humps"; one group with values 0 to 4, another group with values 25 to 30. -- And the worst part is that this belief creates a spiral, because when everyone observed the "two humps" at the adult people, then if some student with starting value 4 does not understand the lesson, we don't feel a need to fix this; obviously they were just not meant to understand programming.

What are those starting concepts that some people get and some people don't? Probably things like "the computer is just a mechanical thing which follows some mechanical rules; it has no mind, and it doesn't really understand anything", but you need to feel it in the gut level. (Maybe aspies have a natural advantage here, because they don't expect the computer to have a mind.) It could probably help to play with some simple mechanical machines first, where the kids could observe the moving parts. In other words, maybe we don't only need specialized educational software, but also hardware. A computer in a form of a black box is already too big piece of magic, prone to be anthropomorphized. You should probably start with a mechanical typewriter and a mechanical calculator.