We had no indication that our son was bored at school other than the fact that he just did not want to attend. I thought for a very long time that it was his insecurity about me not picking him up after school (used to leave scribbled notes in his lunch box to reassure him otherwise). He LOVED to be sick and stay home. His behaviour was never a problem at the school. He never said that things were too easy, that he was bored, that other kids were dumb etc. I never expected that changing schools will make him blossom the way it did. I was proven wrong - thankfully. But one lesson I learned along the way - it is not the school that is the most important here but the teacher. Research what teachers are in store for him next year - try matching his needs with one. Also, I find with my daughter that it really helps to play intelligence down at times - other kids have different strengths. Stimulating him at home at this young age is also much easier than later on, when they mature . I can relate to doing more complex work at home and thinking - why in the world is he waisting his time at school?
Keep searching, talk to other parents in your area, believe me, you are not alone :-)
Ania