My daycare uses the Remind app. Since I'm on Verizon, I received an in app message about this coming down the line the other day. However; my son's Pre-K teacher (who is registered with the county's school system) uses an app called Seesaw Family which is more like a messenger-style app. She has it set up so that only parents and approved extended family are allowed to sign up for her messages. She can send group messages or individual messages as needed and we can send private messages back to her to ask questions. It's free for us (parents) to use, but I'm not sure if she, or her affiliated school, had to pay a setup fee. Apps like that might be worth other teachers looking into.