Hi there
We had this with our daughter over a few years , she was very unhappy and similar to your son (saying she liked school)
she is a very sensitive girl and apart from being ignored by class members some people were also being mean to her. It wasnt a very good school either which didnt help, anyway my advice is to stay in touch with whats happening,
try to open communication channels with your son, he is not telling you what is happening for a reason it may be
* he thinks you will be disappointed that he cannot make friends easily
*he may think you are too busy to listen to his problems and get involved
*he may feel that its his fault that he cannot make friends
An important thing I have done with my daughter is to maintain a very open communication, I know about everything that is going on.
make an appointment with the school and discuss some options, maybe there is a way of changing this, my daughters school did a circle time where they all spoke about their feelings (in little groups) making her classmate aware of how her mean comments affected her life.
(this worked very well!)
be supportive of him, be the person in his corner, it might be good if he tried joining an after school club like football or self defence, this will boost his confidence
and finally always show him that you are listening, (Im sure you do anyway!!) but this is very important to kids that they know that you are interested in their life,
If they are happier then they will settle down and make friends easier, as long as you keep that communication channel open so he knows he can confide in you then things will improve