Please keep in mind that 8 months is not necessarily long enough to resolve the encopresis issue (almost always the case actually)! Many children suffer with this medical condition for many, many years. It's as they get older that they are better able to handle the situation independently. At 5 years old, I wouldn't say the child is old enough to go solo on the entire situation. I have a 6 year old who has been suffering from this condition for 3 years now. He often doesn't know he's had an accident and then, without adult intervention, he'll sit in his feces all day. I have to rely on the support of the school and the before/after school care staff since I work full time an hour from home. This is a battle for me. They are absolutely unwilling to help him the way he needs to be helped. They brush it off and let him sit in it. The schools need be there for the child and their needs.
It doesn't sound like encopresis is the whole problem here.
As you probably know, encopresis is caused by stretching of the colon and loss of colon control after a long history of constipation. Fecal matter slips out and it is beyond the child's control. Removing any impacted feces and getting the child on a very high fiber diet to reduce further constipation is the treatment.
It sounds like a great deal of his problem isn't this physical stretching and incapacity to hold feces - it's his refusal to use the toilet at school. So if that's the case, the doctor's care for constipation won't change the outcome of this child's soiling his pants every day.
I agree with Annie that it would be good to have a discussion with the parents and principal and even counselor - to get a better idea of how long term this treatment is going to be. If the doctor and parents feel this will be resolved in the next few weeks, that's one thing.
It's hard to believe that "serious issues with toileting" will be ale to be resolved quickly.
I am very glad he is under a doctor's care, and hope the doctor is someone who knows something about encopresis. (Unfortunately, a lot of pediatricians don't. Is there any way to ask the mom if the child has seen a pediatric gastroenterologist? If he is still having the leaking characteristic of encopresis, it would seem he still has compacted material in the bowel, and getting that out of there should be a doctor's first concern, that plus stool softeners.)
Anyway, for the kid's sake, I would bring this to the attention of the principal, and have a meeting with the principal and the child's mother. Tell them that the changing thing is acceptable to you (after all, it's better than having him wear a soiled pull-up all day long) but you are beginning to think that having the problem be noticed by the other kids might become a social issue that chases him through his life at this school. Ask what the prognosis is, because you are worried that if it takes a long time for him to get better, he will come away with a bigger problem than he has now.