Colleges' decisions are based on a number of different factors. Some of those, such as their need to meet certain quotas, may be out of an applicant's control.
Assure your child that a rejection letter just means they weren't a good fit for one particular college. It by no means indicates they've failed or that they're not "college material." Don't treat a rejection letter like a disaster, and remember that your reaction will influence your child's reaction. Some school counselors say that they notice many parents take rejection harder than the students.
Hopefully, your child applied to other schools as well -- most counselors encourage students to send out "back-up" applications -- and will be able to continue to pursue their goals. If they accept the school that accepted them instead of dwelling on the less successful applications, they can make the most of their educational future.
If your child is extremely upset about the rejection, they could appeal through the college's admissions office. However, it can be tough to reverse a decision successfully. They could also ask the college about being put on the waiting list.
Some colleges will provide feedback on why an application was rejected. This can be a learning experience for high school seniors, and can help them face future applications -- even employment applications -- in their future.
If your child is willing, they could call the admissions office to find out what they were missing in their application. Although it might be tempting to defend your child, it's important that they make the call, not you. They can use the opportunity to show the college that they're willing to listen and learn.
It's often possible to take what they've learned and apply as a transfer student in a following year after some time at another school bolstering their GPA or working on other weaknesses.
If your child wasn't accepted by any schools, encourage them to talk to their guidance counselor. There are a few options available, including talking to the schools about reapplying.
Students with the determination to succeed can thrive at any school. A rejection letter doesn't have to be the end of the road, but can be a new beginning.