UNAUTH PENETRATION OF CLASS D AIRSPACE ALLEGED BY LCL CTLR AFTER FREQ CHANGE LATE.

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MY STUDENT AND I DEPARTED TORRANCE ARPT ON A NIGHT TRAINING FLT AT APPROX XX05 PM HRS. WE OBTAINED A SHORELINE TRANSIT FROM TORRANCE TO SANTA MONICA ARPT FROM ATC-SOCAL APCH ON 124.30. SINCE ANOTHER ACFT WAS GOING TO SANTA MONICA UNDER SOCAL CTL; WE WERE ASSIGNED AN ALT OF 3500 FT MSL AND CLRED INTO AND THROUGH THE LA CLASS B AIRSPACE. THE SECOND ACFT WAS ASSIGNED 4500 FT MSL. THE OTHER ACFT; A PIPER CHEROKEE; PASSED OVER US AND WAS THE FIRST TO BE CLRED TO CHANGE FREQ; DEST SANTA MONICA ARPT. AT APPROX XX30 PM HRS WE WERE CLRED TO CHANGE FREQ; DEST SANTA MONICA ARPT. MY STUDENT GOT THE CURRENT ATIS; PROMPTLY; AND WENT TO TWR FREQ. WE STARTED OUR LET DOWN IN THE MARINA DEL REY AREA; A DISTANCE OF APPROX 3 NM FROM THE SMO ARPT. THE TWR OPERATOR STATED THAT WE WERE IN HIS 'CLASS C AIRSPACE' AND THEN CORRECTED TO STATE THAT WE WERE IN HIS CLASS D AIRSPACE WITHOUT HIS PERMISSION. I STATED THAT WE HAD JUST BEEN RELEASED FROM SOCAL ON A SHORELINE TRANSITION TO SANTA MONICA. I AVERAGE 2-3 TRIPS TO SANTA MONICA PER MONTH; MOST OF THEM BY SHORELINE TRANSITS UNDER SOCAL CTL. CUSTOMARILY WE ARE HANDED OVER TO THE TWR AND CONTINUE INBOUND TO ENTER THE PATTERN AND LAND. THE EVENT DESCRIBED HERE IS THE FIRST TIME THAT A TWR OPERATOR ACTED AS THOUGH OUR ARR WAS IMPROPER. I CAN ONLY ASSUME THAT THERE WAS SOME CONFUSION AND THE TWR DID NOT REALIZE THAT THERE WERE 2 ACFT INBOUND VIA THE SHORELINE TRANSIT. I ALLOWED MY STUDENT TO MAKE HIS TFC PATTERN ARR IN GOOD FAITH; BELIEVING THAT WE WERE RECEIVING A HDOF FROM ONE CTLR TO THE NEXT ONE. IF THIS IS NOT AN ACCEPTABLE PROC; I WOULD APPRECIATE HAVING YOU MAKE A BRIEF COMMENT IN 'CALLBACK' OR DROP ME A LINE CLARIFYING ATC'S OBJECTIONS.