One of the best ways to inspire and share ideas is to give prizes.
Therefore, I recommend having a regular (example every term) competition for schools. Even a small prize (£20-£50) would be an incentive.
This would generate publicity and create a pool of ideas to inspire newcomers.
Just throwing out the idea for consideration. I won't be offended if you shoot it down. I appreciate that there are some obstacles to overcome...
The first is funding. I propose that the Rpi shop (when it is opened) should have an item "Sponsor a school competition" for sale at £1. I would certainly by one.
The second is financial. Is the foundation willing to administer the prize fund?
The third is logistical. Who would judge the competitions and host the necessary web resources?