*67 doesn't block all caller ID so it is definitely *NOT* the choice for stealthy pranking... 800 numbers and many business lines can see the caller ID even if you *67 and there are tricks if the person you called is using voip where they can see your number. Also if the person you called dials *57 to initiate a Call Trace and then files a complaint with the cops (which seems to be what happened) the phone company will release your number to the police and you will get a phone call.
op diverting or using a service such as $poofcard is better... setting up your own asterisk box is best of all...
Also... get f**king caller ID for yourself... why wouldn't you have it?!?
Soundboard pranks are f**king lame...
And.. invest in some heroin and a gun and shoot up yourself and your school in no particular order... yeah.. that about covers it.