Once kids come into HS/Middle School at least now in 2019/2020, most if not all use personal emails and external chatting apps (most likely Messenger if not Instagram Messages or Snapchat). Compounded with psuedonyms, it's hard for any AI to determine who's chatting who... and even if FB/Snap knew who it was, I'm somewhat certain they wouldn't do anything.
However, in Elementary school, email and Hangouts was the way to go (experience from siblings and myself around 5 years ago), so I guess Gaggle's "AI" can determine if elementary and some middle school kids are a "threat".
Regardless, kids nowadays are really into "self-deprecating jokes": "I want to KMS" or other abusive/harmful messages which a good majority use as jokes (in my experience) although they don't have any wrong intentions. I think any AI or NLP model to determine which is a credible threat and which isn't will be extremely hard to tell, even for humans who aren't teens.