My son went into his three-year-old preschool class reading, but it was still a great experience. He learned social skills, especially what to do when another child "wrongs" him in any way. His preschool had lots of music, arts and crafts, a great playground, lots of hands-on-science experiences and sensory experiences that were all wonderfully beneficial for him. He gained confidence, independence and learned to try things that he saw other children attempt that he did not want to try at home with me (fine motor and sensory).
I personally wouldn't ask the school to meet his reading needs at age 3. I might however ask that they be watchful for any resistance on his part towards doing an activity that he's already mastered ("find the letter A") and be ready to brainstorm alternatives.
