As a teacher, it would be neat to see a messaging feature within classrooms. It would be nice to be able to send a chat or message to students either as a whole or individually for those students who need reminders or those who are excelling and going above and beyond their assignments!
Do you mean one way (teacher to students) or group chat?
If one way, perhaps you could use your school's email system if they have one.
If group, then perhaps zoom, Google Hangouts (both support audio/video/text chats) or Slack (text only) would be a good solution for you.