Often parents are the last to know when their college kids run into academic difficulties. Grades no longer show up at home, profs don't send progress reports and unless your child has signed a privacy waiver with the university's administration office, they won't tell you your child is flunking out. So by the time you discover your child is in academic trouble, he may be far beyond a single failed grade.
He may be facing academic probation or worse, dismissal.
While it's natural to feel angry and hurt - you'll probably wonder why your child didn't say anything before this, or whether he's been lying about his grades - it's also important to avoid recriminations. You may want to rant, but it won't help the immediate situation and there's too much that needs to be done now.
Academic probation serves notice that something has gone very wrong - poor time management, inadequate preparation, academic weaknesses or poor writing skills, for example. But the problem can involve flawed priorities, excessive partying, or even the emotional fallout of hazing. Or, it might involve undiagnosed learning issues, an attention deficit or medical issues that have gone unrecognized. The notice of probation starts a semester-long clock. Your son or daughter has 10-15 weeks to figure out what went wrong, diagnose the specific problem and change direction.
Don't call the university. If your child is 18 or over, privacy laws prevent the university from divulging or discussing anything concerning his academic standing - or anything else. Plus, they don't want to hear from Mommy and Daddy. They want to hear from your child. Your role, as a parent, is to support and guide your young adult along this path, not a helicopter in.
That starts by having a frank discussion of the issues that caused the problem(s) to begin with, figuring out what - if any - outside help is in order, and developing a plan to address it. The university has resources that can help, including a learning center with tutors and study skills instructors. If it's an issue of partying, you should be considering whether there are substance abuse issues as well. And while it's true that attention deficit issues and learning disorders are usually diagnosed in elementary school, some bright kids manage to fly under the radar, only to have those issues become suddenly, glaringly problematic in the less structured environment of college.