I think they could expand whatever after-school programs a lot of these schools have in place. In Johnston, ours is called KTC (Kids-Teen Connection), & is primarily staffed by high schoolers. It's open before/after school, non-school days during the year (in-service/etc), as well as summer. Shouldn't be too difficult to keep that going for that 5th weekday if you were to go to a 4-day schedule. It'd be an extra ~$100-150/month for those that need it - not ideal, but not necessarily the end of the world, either. Not suggesting that would work for every district & every student, but it'd help for most.
As others have mentioned, it'd be a lot easier if corporate America adjusted to a 4-day work week, too.