It can be normal for a teen to find some classes challenging, but if a teen has problems in school, as well as frequent absences or skipped classes, he or she may be demonstrating signs of depression and would most likely benefit most by

Talking with a counselor.

Explanation:

Depression is a serious and debilitating disease. The person suffering from depression does not have the strength to continue with their daily activities such as working, eating and even bathing, for example. In the case of adolescents with depression, the most neglected activity is school. These teens may have frequent absences or skipped classes coupled with intense sadness and uncontrollable discouragement.

In this case, the best thing for a teenager to do is to seek guidance from a professional who can advise them on what to do to remedy their depressive condition. The best professional to do this is the counselor.