Here’s the page with instructions:

https://www.cusd80.com/SchoolMessenger

In summary, to receive texts from SchoolMessenger, you would need to opt in by texting Y or YES to 67587.   SchoolMessenger will send you a confirmation text to confirm that your phone can receive texts from short code.  If you don’t get this confirmation text, please refer to https://www.cusd80.com/SchoolMessenger for how to unblock short codes.