I do understand your husbands concern, but agree that elementary teachers and principals will be much more amenable to reasons related to social or emotional deficit as opposed to academic or intellectual growth for kids who are ahead anyway.
However, the teacher has actually suggested a positive wording which does not allude to a deficit at all - "really help each other and work very well together" - you may run the wording your request by her next time you volunteer, sort of casually, just to be sure you've got it right in edu-speak, KWIM? As an administrator, I'd think "anything that makes a classroom run more smoothly".
Really, it should be a non-issue.
