FLT INSTRUCTOR OF A C172 ORDERED HIS STUDENT PLT TO GAR AFTER OBSERVING A BEECH BONANZA; BE35; TURNING BASE LEG IN FRONT OF THEM WHILE THEY WERE ON FINAL TO AN UNCTLED ARPT.

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THIS WAS A DUAL INSTRUCTIONAL VFR FLT WITH A STUDENT PLT TO NEARBY DKB ARPT TO 'POLISH UP' THE STUDENT'S LNDGS. MODERATE SSW WINDS FAVORED RWY 20 AND CTAF INDICATED OTHER ACFT IN PATTERN TO RWY 2. WE (ACFT #1) ENTERED L TFC TO RWY 20 ON THE 45 DEG ENTRY TO THE DOWNWIND; COMPLETING SEVERAL (3) CIRCUITS. TFC WAS MODERATELY BUSY WITH 2-3 ACFT IN THE PATTERN; INCLUDING ARRS/DEPS; AND PRACTICE INST APCHS. WE (ACFT #1) WERE SELF-ANNOUNCING ON CTAF AND COORDINATING WITH OTHER ACFT; ESPECIALLY THOSE ON PRACTICE APCHS. OTHER PLTS WERE ALSO MAKING GOOD USE OF CTAF. AFTER TURNING FINAL TO RWY 20 DURING ONE OF OUR CIRCUITS; MY STUDENT AND I SIMULTANEOUSLY NOTICED A V-TAIL BONANZA (IN THE UPPER L WINDSHIELD -- APPARENT POS MOVING LITTLE) ON A HIGH AND CLOSE L BASE TO RWY 20. MY STUDENT INITIALLY STATED TO DIVE DOWN TO RESOLVE THE CONFLICT; THEN I COMMANDED A R TURN AND GAR; WITH A SIDESTEP TO THE R OF RWY 20. I ASSISTED HIM ON THE CTLS FOR THE GAR; AND ANNOUNCED ON CTAF THAT WE WERE GOING AROUND SIDESTEPPING TO THE R TO AVOID THE BONANZA ON L BASE TO FINAL. THE BONANZA CONTINUED TO LAND RWY 20 (LANDED A LITTLE LONG); AS WE CLBED OUT R OF RWY 20 ON THE GAR. BOTH STUDENT AND INSTRUCTOR WERE SHAKEN UP AND STUDENT'S PERFORMANCE ON NEXT CIRCUITS SLIPPED; SO WE WENT FULL-STOP TO DEBRIEF THE SIT AND POSSIBLY TALK TO BONANZA PLT; WHO WAS DEPARTING AS WE REACHED THE RAMP; SO WE WEREN'T ABLE TO ASK HIM WHAT WAS GOING ON -- EMER; ETC. WE DID TALK WITH FBO EMPLOYEE WHO SAID BONANZA PLT HAD SAID THAT HE WAS NOT SELF-ANNOUNCING. ALSO; TALKED WITH PLTS OF A PIPER THAT WAS ON DOWNWIND WHEN THIS HAPPENED AND THEY STATED THEY HAD NOT HEARD CTAF CALLS FROM BONANZA; FELT HE CUT OFF BOTH OF US; AND HAD NOTICED SOMEWHAT ERRATIC ALT CHANGES BY BONANZA.