Regardless of the integrity of the 20% figure, it does show that many young people have needs that aren't being met in terms of their mental health. How does this play out in the classroom? You don't need a doctorate to see that kids with a chaotic internal life often times struggle in the classroom. We all see it. Why? Kids are less likely to take risks or even try when they don't feel confident, safe, and capable.
How can we make our classrooms those places? It's not the decorations. Sure, those may help some kids, but it's about letting kids know it's ok to mess up but not ok to keep messing up. Instead of throwing that zero on them, ask why they haven't done their work and talk through some strategies for dealing with the hardships in their life. If they still don't, THEN throw the zero on them. Kids crave structure and consequences too.
I'm no Cesar Milan. I don't have all the answers. The veterans on my campus told me to talk to my students and not take things personal. That's what I did. That's what I do. That's showing results for me. Now, there are some that won't improve no matter what, but the other piece of advice I received is to control what I can control. I never give up on any of them, but some just can't have all my attention. It's not fair to the rest of the class and it's not fair to that child to think they can always have 100% of the attention of someone else.