I was the same as you. I increase all room prestige to over 3 or 4, started training doctors, upgraded medical unit and lecterns and then I hit it. 

I had a similar issue and had to restart that one over. I found that I managed to get the 1 star target after a while it just took some patience.  I kept both courses to a maximum of level 2 IIRC and kept the campus to just available plots in the first area to reduce the chances of them getting unhappy and keeping the student numbers down so it would be easier to increase the grades. Still took a while.

I do wonder if Spiffinmore is bugged. Getting to 3 stars in that ended up feeling like a massive chore as the amount of students who were very unhappy despite having plenty of facilites to relieve boredom, tiredness, etc., and having high hygiene ratings was insane. I wonder if pathfinding was partly an issue as found that once expanded in to other parts of that map, students took a long walk route in areas you couldn't own or place heaters or anything in so their happiness ended up tanking and ended up with them being cold, bored, etc.