We are dealing with the grade acceleration question too. My daughter started K reading at almost 3rd grade (guided reading level @ M), then when she was tested at school after getting a recommendation from a private test for gifted programming, her reading process is at High School level and she is multiplying and dividing having not been sat down and "taught" more than counting by 2s,5s and 10s ect. So, when we went into the school grade acceleration was presented, and when we talked to her about it, she said "No". I was held back in the 4th grade and did not want to be and spent many years angry and refusing to do my school work. I think that the child's feeling on grade acceleration should be the biggest factor in the decision.
