Unless the student has a learning disability or language problem, I would put much of their unpreparedness on their parents, who should have been paying more attention to their schoolwork.  My parents did, and it worked.  We couldn't do anything or go anywhere until homework was done, anything less than a "B" meant extra time studying, often going over papers and test with parents to make sure we understood why we failed, and we got a lot of coaching if we weren't motivated.  There were 4 kids in my family; all of us went to college but 3 took a long time to graduate; 3 of us graduated high school with GPAs 3.8+, and the other had a reading disability but was a very talented artist who was admitted to college because of her art portfolio, and is one of two with a graduate degree.