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It looks like you've done your homework! Yes, I do not see State-level acceleration policy for Nevada here or here or here.

Originally Posted by Cnm
Is there anything else I can do?
Yes, here are a few things you can do:

1. When a school cites "social/emotional issues", ask them to elaborate. Be prepared for worst-case scenario (which is, for them to nit-pick on each thing a child may have done "wrong"). Keep calm, take notes, jot each thing down, and ask if there is anything else. Once a person is prepared to deal with worst-case scenario, they can deal with anything else. For example (best case scenario), the school may have nothing behind the "social/emotional issues" statement. They may be bluffing... by asking them to elaborate, you called their bluff. Don't gloat, just make a note such as "general concern... nothing specific to my children".

2. You may wish to read up on the IAS. If you've been a frequent reader/lurker here, your eyes may be rolling in your head or glazing over. For that, I apologize... and yet take heart, possibly another parent will read this and find it to be new information. When reading of the Iowa Acceleration Scale on Hoagies' Gifted Education Page, you will see:
... sibling in the same grade, or sibling in the receiving grade. According to the scales, these are critical items, and totally negate the idea of whole-grade acceleration. I disagree there - in my opinion we should always treat our kids as individuals, and though a lot more care needs to be taken, these two issues should not make whole-grade acceleration a total "NO".
If having a sibling in the receiving grade happens to be what the superintendent was referring to as "social/emotional issues", then you are not alone in choosing to ignore the advice of that one particular point in the IAS. More on the IAS and full-grade acceleration here. Roundup of links on advocacy, meeting prep, and school fit here.

3. When you say this 3rd grade teacher was recommended by everyone you talked to, did that include parents of similarly gifted students? Or did you only have the opportunity to speak with various staff members? (Please do not answer that, but only reflect on it, and on how each perspective may be quite different: Parents may be seeking the support and encouragement of their child's development of gifts/talents, while teachers may be tasked with cutting down tall poppies and striving to ensure equal outcomes among all students in their classroom.)

4. Among the resources which you shared with the school, did you share reports from the acceleration institute? ... and the opportunity for teachers to join the Davidson Educators Guild?

5. Lastly, you may wish to contact the acceleration institute regarding your children's situation (especially if the IAS advice to forego acceleration when a sibling is in the receiving grade, may be coming into play as an impediment to acceleration).
The IAS states, in part:
Quote
"4. How important are the age and school grade of siblings when considering acceleration? ... While we have heard anecdotal information that skipping a child into the grade of an older sibling has had positive results, our experience and training in family dynamics speaks against such a move. Although each family is unique, the Belin-Blank Center remains consistent in consulting with schools and parents against a grade skip under these circumstances."
This is just one of 15 issues with case vignettes in the book. Several years have passed since the IAS-3 was published. If the acceleration institute will agree that what may be a good rule in general may not be a good rule for an individual family... possibly the superintendent will reconsider. For example: If the older sibling has a misfortune (medical issue, accident, etc) which may preclude their completion of a grade level one year, would the parents also have the younger sibling held back that year to prevent the two from being in the same grade level the following year?

PS. You may wish to obscure any possibly identifying details in your post (state moved from, state moved to, rural, etc).