>It's pretty complicated to say the least. I was hoping I would be able to write a statement that just checked for a students existence in each subquery. I was thinking of using ICASE but I wasn't sure if I could use that in conjunction with "Where exists ( Select * from level5)".

You can use CASE with EXISTS

CASE 
  WHEN EXISTS (Select 1 from level5) THEN 5 
  WHEN EXISTS (Select 1 from level4) THEN 4 
  ...
  ELSE 0 
END AS StudentLevel