I have seen no evidence that grandfathering siblings would increase transportation costs. Of the people I know--myself included--the majority actually will need to be bussed to their NEW attendance area school, but could walk if they are grandfathered. (We live .3 miles from our current reference school but were drawn out of that boundary). So I don't see a cost savings. To the extent there are transportation costs, deal with that issue by not providing transportation to grandfathered students once their sibling ages out of the school.

Grandfathering siblings is irrelevant at the high school (Garfield or any other one) level. That is because there is a10% set aside for "choice" seats, with siblings as the first tiebreaker. So grandfathering isn't needed.