He can enroll in a self-paced program on the computer or in workbooks to earn the credit he needs for the semester he did not complete. This can be done much more quickly and well enough if he will willing to do the work. Also, the public school may not be a good match for him. He may need to power through online courses or attend a charter school to complete his high school diploma while working part time to get him used to working and give him something else to get his sense of accomplishment from. Please look at the troubles he is having that may have led to this behavior. Is he depressed? Is he bullied? Is he mourning something? Are things going poorly at home? Does he have poor social skills? Not every child's needs are met by the public school, but the parents will need to get actively involved to help him out of this for the sake of his overall well being now and later. A change of schooling method may be just what he needs. Public schools are a blessing, but they cannot meet every child's needs well. Also, there may be alternatives the school knows about, but don't assume they have all knowledge of all the options. They usually will pressure you to keep your child in their system as that is tied to resources for them, but it's not always the best choice. Find out about the options, talk with his parents about them and let him help pick the option that works best for him and then hold him accountable. Make sure his life has some happiness in it and he needs lots of emotional support from family right now in terms of family outings, time to talk, etc. God, give the parents wisdom and the child encouragement to make the right decisions and carry through.