In my time instructing there, supervised solos wasn't a thing. However the school did put a tremendous amount of effort into the solos, they had tons of rules and guidelines, the biggest issue was the students were on a timeline, they had to solo within a certain timeframe and both the students and the instructors knew this. I thought that was the biggest danger, forcing every student to solo in a certain timeframe, because as mentioned by JohnBurke, a handful of these students were not solo ready. How more crashes don't occur is an absolute, hands down wonder.