For what it's worth, from my enroute course seven rated successfully out of twelve initial starters. Of the five who didn't make it, one dropped out about six months into the course, three didn't pass the final sim exam in the college and one missed out during final field training. The last two from my course rated a month or so ago.
Three of the four tower blokes who started at the same time as us finished at the college, they had one pull out voluntarily four or five months into the course. The last of the remaining three rated in January this year, a full six months before the last of the enrouters who started training on the same day. In fact we were just finishing up at the college at the time.