Many years ago, I taught a speedreading course for a company - they did things right,by my standards, (taught to get used to using more peripheral vision, to move eyes down page at regular (constant) speed, tested with questions that required knowledge of the material - though not understanding of it - in all fairness, if someone cannot understand/interpret the material no speedreading course I am aware of will help!).
My speed was 800 wpm w/95+% comprehension when I started and 6000wpm
w/80% comprehension when I started the teaching (they required prospective teachers to take the course - they did not charge for that). Best student that I personally know of/worked with got to 10,000wpm with (minor quibbles) 75%comprehension. This was about thirty years ago in Nashville,TN.
I have no idea if that company still exists and I only worked for them until I got a full-time regular job (about 11 months) but it was American Speedreading Academy.