It's always been a challenge to get students to buy in to an out of class communication tool. Over the years I've tried many including mailing lists, Piazza, Discourse, Vanilla and other discussion forums, Slack and probably a few other things.
I guess it's not surprising that it's a hard sell - prior to the internet once school was out kids there as no teacher student interaction until the next school day and kids would only interact with their direct friends.
Still, we have technology and even without great buy in, if nothing else there's an advantage to having an electronic means of distributing things to students.
Ultimately I fell back on a plain old mailing list. Discussion/forum platforms didn't work for me because it was yet another location that you had to remember to check. Slack didn't work because at its core it's for live chat and while workers are at their desks all day and can have a chat open, that doesn't work with students and catching up on a complex Slack with threads after the fact is, well, just no.
With us going remote in Coronatime needs changed. Slack looked like it might be more viable. It still had the problem of limited threads but in addition to students being more "always on," for better or worse, live remote teaching benefits form a chat. Why Slack over the built in Zoom chat? Well, one thing is that the Zoom chat disappears after the session whereas Slack lives on and can form the base for ongoing discussion. Second, dedicated chat platforms like Slack are more robust and featureful.
Over the summer and into this semester, Slack seems to be working very well for my teacher certification candidates but I ended up using something else - Zulip for my undergraduate classes and plan to move my teachers over to it for the next cohort.
Why the change? Both Zulip and Slack have free tiers but Zulip can also be self hosted and is open source. Slack is slicker when it comes to integrations but Zulip is the clear winner for combined sync and async conversations due to its threading model combined with flexible alerts.
I put together this short video showing the basics - check it out:
You can use Zulip free on their site with similar limits as for Slack's free tier or you can self host. I'm running our Zulip instances on a Digital Ocean droplet. DO has a "one click" Zulip setup that was fairly straightforward. You might want to check that out if you're comfortable as a Linux admin.
So far, I'm liking Zulip very much and thing I'll be using it as my primary in and out of class communication tool. I'd like a better selection of emoji and wish it was easier to both use integrations and write bots but the thread based interface is really great.
I know Slack's the big name and I do like Slack as well but if you're a teacher and looking for an in and out of class chat/communication platform check Zulip out.