Start by deeply thinking though the problem that you current customers have and how your software solves it.
You must know other schools that are similar to your current schools. Where can you get a list / LinkedIn? / Government ed sources / Buy a list.
Write materials to contact these schools / emails / newsletters. Keep cold contacting them every 3 - 12 months (unless they ask you not too).
For groups who response with queries, setup time to show them your solution. Give them testimonials.
If they ask for a sales pitch, then offer to quick config your solution to their local needs.
It's a process of talking to potential clients, discovering and understanding their problems, and considering how your software could be a solution. It is a conversation.
As the founder you need to sell, sell, sell. Oh did I mention sell?
You need to develop a sales cycle, that means everyday picking up the phone and cold calling, any interested leads get followed up to a schedule 3months, 9 months, 24 months, build out your marketing emails, write monthly blog posts and post to linked in.
Are you attending education conferences?