seek out an independent advocate
While an independent advocate can be a great resource for those who can afford it, often parents are their children's best advocates. There are several resources with advocacy tips in
this recent post. This might be your best path toward establishing your child's "need" for advanced academics.
It seems your child had a formal eval from which a GAI score was posted earlier... often a GAI is indicative of slower processing speed and/or lower working memory, which could possibly be impacting your child. Have you checked with the person who evaluated your child to inquire whether his/her interpretation of the assessment results might reveal anything which the teacher could be painting with a broad brush as "immaturity"?
Also, have you asked your child for input as to how he sees the reading time? For example, if he is pulled out alone, does he feel uncomfortable in being isolated? Are there specific things which he can articulate which are "triggers" for the described behavior?
