After you've confirmed that a school is interested, you need to set up an initial meeting. This can be over the phone if necessary, but ideally you should go into the school and meet the member(s) of staff you'll be liaising with.
What to say
When you meet with the school, introduce yourself and say that you're a volunteer mentor with Design Club. Explain that Design Club is a non-profit social enterprise and that the club will be free for the school to run. (Design Club resources are published under a Creative Commons licence which means they must not be used for commercial purposes.)
Tell them the children will be designing and prototyping a helpful mobile app. Explain that Design Club is not a coding club, but that the children will be learning useful creative skills that will help them find future jobs in digital and technology.
You may want to show the school one or all of the following:
Once the school has agreed to host a Design Club, you may want to start thinking about How to promote your club