We had similar issues with one of ours, in an academic K4 (though the peer social situation was a bit better). It turned out that part of the issue was temperamental (just wanted to be home with parents), part of it was the schedule (too early, and too long a day), and part of it was the child's expectations. Presented as "school", (vs day care) there was this assumption that there would be learning involved. When there wasn't, there was deep disappointment.
It didn't help that older sib's idea of "preparing for preschool" the summer immediately previous consisted of high-interest, positive-reinforcement-loaded, fast-paced, individual instruction in first-grade reading and math, which was so well received that I had to chase them to bed at 8:30 at night, after literally hours of "playing school".
It took us quite a bit of the school year, and many conversations and observations, to figure out that these were some of the issues. The school didn't see any of it, because the little rule-following, people-pleasing person was very careful to precisely meet every expectation there.
