One day last spring, Marianne Recher saw an organic produce delivery truck pull up at the West Marin School and was overcome with joy. To the delight of the driver, she started snapping photos as he pulled out a box of fresh strawberries.

“This is amazing!” she exclaimed. “You’re delivering to our school! This food is going into our kids’ bellies!”

Such deliveries have become more frequent this year as four tiny West Marin districts—Shoreline…