To wish our school, you could say:

"I wish our school a bright and successful future."

"I hope our school achieves great things and continues to thrive."

"Here's to a wonderful and prosperous future for our school."

"I send my best wishes for the continued growth and success of our school."

These are just a few examples, but you can use any language that feels appropriate and genuine to you. It's always nice to express positive sentiments and encourage success, especially when it comes to educational institutions.