I wholeheartedly agree with blackcat's suggestion of going in to observe/help out in the classroom at the beginning of first grade. I wish I had not waited until November of first grade to do that.
That way you can see with your own eyes what the teacher is seeing and provide useful information based on your unparalleled knowledge of your son.
I took one look at my son inhis classroom environment and could tell he was extremely stressed, to others he just looked neurotic and quiet, which probably fit their expectations just fine since he has aspergers. He was seriously underacheiving academically and regressing in autism behaviors.... but doing so quietly and cooperatively so no one noticed but me.