
SCARY
No parent ever wants to deal with this situation, but since you've been thrown into it's in your lap. You can handle this, but make sure that you cover all your bases and don't let any detail slide under the carpet.
Start a log of exactly happened with all dates included with phone numbers and people involved.
Call the principal/headmaster of the school and make sure that the school counselor has been notified. Ask if the counselor is a college counselor or a behavioral/academic counselor. Ask if this is a counselor with a master's degree in psychology, not a person assigned to counseling with a non-behavioral trained degree (like a degree in education.) Many schools have an off campus policy of behavior (esp. if it is a private school.) Ask the principal, "What are all of my options?" We don't need another school massacre and we already have a threat.
Make sure that all phone numbers on both kids text/phones have been changed and private numbers are now a must.
Contact all parents of the kids involved with a scripted and gently concerned statement about calming the kids down and a question proposed what can we do to keep the kids away from each other and resolve this problem. Obviously the other boy's parent is the one you are concerned about - who are they to produce a kid that much in trouble.
Ask Jenna's parents what their plan is and be united with them. Are we sure that Jenna has not provoked this for the drama? If she did she may have been surprised at what their response was to her. Don't be afraid to tell your son that it may be time to cool it off with Jenna for a while and protect himself. If he says, "mom, you're overreacting, and then your gut will tell you that you are right."
Ask the police which department specifically will be assigned to this case and who you can stay in touch with and what are your options.
Keep asking each person you talk to: "what are all of my options and what am I overlooking to keep my son safe." Then ask, "What does my son need to do?"
Your son, while being a really good kid with a high EQ (emotional quotient) cannot project the possibilities with his brain. Kid's frontal lobes of their brains do not develop until they are 21-23 and the frontal lobes are what they need to use to deal with reason and judgment. Boy's develop later than girls. So, he needs to be included in the process, but you need to remember that he cannot project the way we can based on our own vast history of experiences.
OK, those are my suggestions. Can you tell that I work in 50 of the most prominent schools in CA? I was lucky to sit in a lecture and get to know the leading crisis response team manager for school massacres in the country at one of the schools I work in in Beverly Hills.
Good luck, let us know how it works for you and don't stress eat. Your blood pressure is raised because of this, so no salt and stick something healthy and crunchy in your mouth to reduce your blood pressure (carrot, celery, nuts and Dr. Oz's recommendation breath strips.)