There is a separate law that is only for k-12 school campuses.
626.10. (a) Any person, except a duly appointed peace officer as defined in Chapter 4.5 (commencing with Section 830) of Title 3 of Part 2, a full-time paid peace officer of another state or the federal government who is carrying out official duties while in this state, a person summoned by any officer to assist in making arrests or preserving the peace while the person is actually engaged in assisting any officer, or a member of the military forces of this state or the United States who is engaged in the performance of his or her duties, who brings or possesses any dirk, dagger, ice pick, knife having a blade longer than 21/2 inches, folding knife with a blade that locks into place, a razor with an unguarded blade, a taser, or a stun gun, as defined in subdivision (a) of Section 244.5, any instrument that expels a metallic projectile such as a BB or a pellet, through the force of air pressure, CO2 pressure, or spring action, or any spot marker gun, upon the grounds of, or within, any public or private school providing instruction in kindergarten or any of grades 1 to 12, inclusive, is guilty of a public offense, punishable by imprisonment in a county jail not exceeding one year, or by imprisonment in the state prison. [Ed. Note: This is the paragraph dealing with legal carry on K-12 school grounds.
Right, that limits things. Non-locking utility knives less than 2.5 inches. Wenger or Victorinox Swiss Army knives (careful some of the Wenger ones lock, most of the Victorinox are to long), a Scout type knife (Case makes some nice ones, though again they might be a little long), a stockman, pen or trapper could be ok (again though length might be an issue).
I think though that you should ask your son what kind of knife he wants, if he doesn't know then you can show him some pictures of knives (go to the manufacturers sites, Wenger, Victorinox, Case, Buck, etc.) and let him pick. Make it a big deal, kind of a ritual of adulthood ("You are 16 now, you are responsible, I trust you, you can make life choices now."). This will make him proud and happy, and also it will make him more likely to not abuse the knife (ie break it doing something stupid, trade it for something, threaten someone with it and so on).