BE33 PENETRATED CLASS B AIRSPACE AT PHX WITHOUT CLRNC.

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WHILE INSTRUCTING A PVT PLT WORKING ON A COMMERCIAL CERTIFICATE; I GAVE HIM A PROB TO SOLVE. DEPARTING SDL OVERFLYING FFZ ENRTE TO LAND AT IWA; I HAD THE STUDENT CLB TO 3700 FT MSL. WE HAD PREVIOUSLY DISCUSSED THIS SIT BEFORE THE FLT AND I POINTED OUT THE PHX CLASS B AIRSPACE AND HOW TO STAY OUT OF IT. UPON DEP FROM SDL; I TOOK CTL MOMENTARILY AND HEADED TOWARDS FFZ. THE STUDENT TOOK CTL AND REFLECTED THE ROUTING WE DISCUSSED EARLIER. FEELING COMFORTABLE WITH THE STUDENT'S AWARENESS AND INITIAL TURN; I BEGAN GETTING ATIS FOR FFZ AND IWA. I THEN CONTACTED FFZ WITH A COURTESY CALL AS I KNEW WE WERE ABOVE THEIR CLASS D AIRSPACE. IT WAS AT THIS MOMENT THAT I DISCOVERED WE HAD CUT THE NORTHERN CORNER OF THE PHX CLASS B AIRSPACE WHICH BEGINS AT 3000 FT MSL; NORTHERN LIMIT ALONG INDIAN BEND ROAD BTWN PIMA ROAD AND GILBERT ROAD (APPROX PXR 040 DEG RADIAL 10 DME). I IMMEDIATELY MADE A L TURN BUT IT WAS TOO LATE. DURING THE DEBRIEFING; I HAD A LENGTHY DISCUSSION WITH THE STUDENT. HE STATED THAT HE THOUGHT 'I' WANTED HIM TO FLY DIRECT TO FFZ. I INFORMED HIM REGARDLESS OF WHAT HE THOUGHT 'I' WANTED; IT WAS HIS RESPONSIBILITY TO AVOID CLASS B AIRSPACE WITHOUT PROPER CLRNC. THIS IS A TYPICAL SIT OF THE STUDENT TRYING TO BE CLAIRVOYANT AND NOT PRACTICAL. NEEDLESS TO SAY; I WILL BE MORE OBSERVANT OF WHAT IS HAPPENING DURING CLASS B AIRSPACE TRANSITIONING.