BE76 FLT INSTRUCTOR DOES NOT FOLLOW UP ON INFO PROVIDED BY STUDENT WHEN DEPARTING IWA ARPT AND CLBS INTO PHX CLASS B AIRSPACE PRIOR TO REQUESTING CLASS B ENTRY CLRNC.

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ON THE DATE AND TIME DESCRIBED ABOVE; MY STUDENT AND I INADVERTENTLY ENTERED CLASS B AIRSPACE WITHOUT CLRNC. WE MADE FLT INTO WILLIAMS GATEWAY ARPT ON AN IFR FLT PLAN UNEVENTFULLY AND OPTED TO DEPART VISUALLY FOR THE RETURN FLT. PRIOR TO DEPARTING WILLIAMS GATEWAY; I QUESTIONED MY STUDENT ABOUT THE CLASS B AIRSPACE BOUNDARIES AND HE STATED THAT THE FLOOR DID NOT BEGIN UNTIL 6000 FT IN OUR AREA. WE DECIDED THAT LEVELING OFF AT 5000 FT WOULD BE A GOOD PLAN IN ORDER TO REQUEST OUR CLRNC. HAVING FLOWN INTO THE AREA ON NUMEROUS OCCASIONS; I KNEW OR I ASSUMED I KNEW THAT 6000 FT WAS INDEED THE FLOOR OF THE CLASS B AIRSPACE. HOWEVER; I HAD TAKEN 5 MONTHS OFF FROM FLT INSTRUCTING AND WHAT I DID NOT REALIZE WAS THAT THE AIRSPACE HAD BEEN REDEFINED. WHAT USED TO BE THE FLOOR AT 6000 FT HAD BEEN LOWERED TO 5000 FT. THIS CHANGE OCCURRED APPROX 2 MONTHS PRIOR TO MY RETURN. THANKFULLY; THERE WERE NO ADVERSE RESULTS FROM OUR TRANSGRESSION; OTHER THAN BEING CHASTISED BY ATC. I BELIEVE THAT CONTRIBUTING FACTORS TO THIS INCIDENT WERE COMPLACENCY ON MY PART FOR ASSUMING THE AIRSPACE BOUNDARIES HAD NOT CHANGED DURING MY HIATUS; AND MY FAILURE TO SUPERVISE MY STUDENT MORE CLOSELY. AS MY STUDENT WAS CHKING HIS VFR SECTIONAL; I SHOULD HAVE BEEN CHKING IT WITH HIM!