While I am still using (and satisfied with) the original version, Remind has recently added School and District plans.
I highly recommend you check out Remind if you haven’t yet!
It is extremely easy to add people to Remind. Printable PDFs are available with directions, a link can be sent, or you can add people manually with their phone number or e-mail.
In order to access the Remind app, your device must have access to the iOS store or Google Play, or there is also a desktop version for Macs. The app is not required, though, as reminders can still be sent via text message and/or accessed via the website at www.remind.com.