I've been developing educational software since the punch card days, and spent my (painful) time with Flash/AS. I utterly despise it, and what the vast majority of people used it for. However, Flash still has a lot of advantages for online software that is intensive (heavy CPU due to complex graphics, accurate animation speed, keyboard response time importance while animations are happening, dynamically changing many things on the screen simultaneously, 3D, etc.).
We recently hired a company in India (we didn't have 20 spare developers in-house) to convert 20 years of online math/science simulations to HTML5. That was completed last year, although a few of the simulations are still really sluggish on some computers. Also, not all browsers/tablets support 3d WebGL content. Schools tend to be two to three years behind in technology which also makes things tough.
We are continuing to migrate our most complex product to HTML5, and building all new products that way. It is still a giant challenge to get the functionality we want/need in the product, but HTML5 will continue to improve and it is the only option moving forward (at least for the near future).
I hate Flash, but it does still have a place in the world. In two years it will be gone in a very rapid "flash." In my opinion.