What does it mean it’s now a regular series? Was it not before?
When the series first started, it launched in the
Jump Rookies label - which is something Jump+ does where users can submit their own manga to the site, and the ones which get the best views and scores are posted to the main site. Think Manga Plus Creators and you’re halfway there.
Ultimately, Kindergarten Wars got so popular that Jump officially promoted it to being a full serialization. Which means that Chiba-Sensei gets an official editor, it gets print volume releases, the whole nine yards.
This makes Kindergarten Wars the second Rookie title to become a full-fledged serialization, after
Red Cat Ramen. Although ironically, both authors previously had works published in Jump+ as actual serializations (Dricam and East Into The Night were even translated on Manga Plus), so this was mostly the equivalent of a famous comic artist starting an indie webcomic and then their old publisher calling them and going “you wanna shack back up again?”