Wireless Access

First of all, is it necessary to ground an AP275 mounted to an exterior brick/concrete wall of a school?

If so, what do I ground to if no conduit is present?  My thought is to run a ground wire back through the penetration in the wall made for the ethernet cable and attach the ground cable to red iron in the ceiling via a grounding clamp.  Another potential problem is on some sites the AP has to be mounted to a covered walkway, these areas are not easily accessable as say a ceiling.  Making running the cable back thru the penetration and attachinb the ground cable to some part of the metal structure very difficult if not impossible.  Any thought or ideas would be greatly apprieciated. 

Yes, all outdoor installations should be grounded.

I'd shoot for an actual earth ground rather than use the building.  I'm not an electrician, but that would be my preference and always what I do.

It really is best to consult with your local CE/electrician as to the best method to grounding, as different areas have different codes, and should an event occur and proper installation rules weren't followed could cause issues later on.

Taking the ground into the building does have some risk as it can provide a path into the interior building (which is one thing grounding should avoid). So Aruba's advice is seek local CE expertise on grounding rules and requirements.