I think it's important to stress right from the start of the very first week that as instructors we are here for the students and want to support them. They should email, call, chat, whatever us whenever they are struggling. This is why we teach. If they don't learn, we aren't doing our jobs. I think it's important to students to understand that they aren't "bothering" us when they contact us. Weekly reminders of this might really serve students well.
