I've been thinking about the same thing myself.
Title 11, Chapter 5 states this:
§ 1442 Carrying a concealed deadly weapon; class G felony; class D felony.
A person is guilty of carrying a concealed deadly weapon when the person carries concealed a deadly weapon upon or about the person without a license to do so as provided by § 1441 of this title.
The underline is my emphasis. To be guilty of section 1442, you must both conceal the weapon and lack the license. If you do not have a weapon, clearly you cannot be in violation of section 1442. Likewise, if you have the license, as provided in section 1441, you are also not in violation of 1442.
Further down, Title 11 also states this:
§ 1457 Possession of a weapon in a Safe School and Recreation Zone; class D, E, or F felony; class A or B misdemeanor.
(a) Any person who commits any of the offenses described in subsection (b) of this section, or any juvenile who possesses a firearm or other deadly weapon, and does so while in or on a "Safe School and Recreation Zone" shall be guilty of the crime of possession of a weapon in a Safe School and Recreation Zone.
(b) The underlying offenses in Title 11 shall be:
(1) Section 1442. — Carrying a concealed deadly weapon; class G felony; class D felony.
(2) ...other offenses
I've snipped the rest of the offenses in subsection (b). You should go read them yourself to make sure you aren't planning to violate any of them. They include items such as destructive weapons, switchblade knives, knuckles-combination knives, martial arts throwing stars, and other unpleasant things. The part that concerns me is the first offense outlined in subsection (b). It is "carrying a concealed deadly weapon", as defined in section 1442. Well, we've already established that you are not in violation of 1442 if you possess a valid license as provided by section 1441. Of course, we also need to remember the "enforcement" part of "law enforcement". If the police show up, they are not "law interpretation". That job is left for the judge in court, and he or she may not read Title 11 the same way as I.
As others have already stated, if the representatives of the establishment (whether it be a school, the Christiana Mall, or any other self-professed "gun free" zone) request that you leave the premises, it is highly recommended that you do so respectfully and immediately. Don't get yourself caught up in a trespassing charge.
You should review Title 11 yourself. Here is a convenient link:
http://delcode.delaware.gov/title11/c005/sc07/I'm not a lawyer, your mileage may vary, and these are trained professionals. Kids, don't try this at home.