Who are you communicating with about this at the school? My advice having previously worked in a school environment is to raise it directly with the Senior Leadership Team and/or Headteacher (not the class teacher). Producing a knife at school is not a trivial matter and should be taken seriously by them. 

 I'm not at all doubting your intuition. The problem with intuition is that it gets clouded when fear creeps in.

I suspect that your intuition tells you that this kid is unhinged/dangerous. This feeling combined with the shit on the news brings about a sense of fear (understandably).

All I'm saying is to try and let that fear go before taking any action from here.

Involving LE could make the whole situation worse (this is a woke world still).

You could withdraw your son from the school but that would impact your son & your relationship with him. 

It's a shitty situation but there are no coincidences. This kid has entered your reality to teach you both something.

💚 

 It’s great advice.  I’d love to just withdraw him, but you are right that there is a lot to consider. The opportunities he is receiving from his school athletics is a huge factor. Thanks for making me step back and think instead of being reactionary from the get go. It does look like the school is requiring a psychological evaluation of the student which is at least a step in addressing whether this kid could harm others or himself.