Hard to tell, there are so many factors involved:
whether this is a bad school
whether there is bullying involved
whether the child in question is going through a bad phase
whether the child in question is the kind who is going to say he hates something every time he finds it difficult
whether the child in question is likely to say he hates something because it is the cool thing to say
whether he is genuinely upset or not
whether he is upset all the time or just likes to come home and offload after a bad day
whether school actually is the right solution for him or not
With my own children I do know because I know them. Dd had a hard time at junior school (awful head, discrimination) but still wanted to be at school. She is now very happy at secondary, though if she is tired she will still occasionally sound as if she hated it and everybody. And moments when she is clearly repeating Cool speech. But there are more bubbling moments than hating-everything moments.
Ds who is at junior's would never willingly admit that he likes school or sees the point of it (very uncool), but I can see for myself that he is not miserable immediately before or after school, and that he is miserable when he has to stay at home.
If either of them looked constantly unhappy, I would re-think the whole figure.