Extension of visa for Gap student working at a Chinese school

Can you please advise me, on behalf of my son who is currently in Yantai, as a Gap student. He was given a 6 month visa which will expire in July. He has been told that he needs to leave the country to renew it, but there seems to be conflicting advice regarding this matter. He was also told he can renew it in Hong Kong, but a previous posting on this site says otherwise. Can you please advise! He plans to visit a neighbouring country/countries during the summer anyway, but will need an extension when he returns to complete the year teaching.