STUDENT PLT OF AN SMA SINGLE ENG LAND ACFT TURNED DOWNWIND IN FRONT OF RPTR'S ACFT CONTRARY TO ATC INSTRUCTIONS RESULTING IN AN NMAC.

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WE ENTERED THE PATTERN AND DID A TOUCH AND GO TO STAY IN R CLOSED TFC. ON THE UPWIND LEG; THE CTLR TOLD US THAT WE WERE FOLLOWING THE SECOND HELI ON DOWNWIND. 2 HELIS WERE ON R DOWNWIND; AND WE HAD THEM BOTH IN SIGHT. THE SECOND HELI WAS AT OUR 2 O'CLOCK; SO WE PROCEEDED UPWIND; PLANNING TO MAKE OUR TURN TO XWIND WHEN THE HELI WAS ABEAM US. THE CTLR TOLD AN SMA SINGLE ENG LAND Y WHO WAS ALSO IN THE PATTERN TO FOLLOW US; WHICH THE PLT ACKNOWLEDGED. DUE TO NOISE ABATEMENT AND SJC'S CLASS C AIRSPACE; LCL PROCS CALL FOR A 20 DEG TURN TO THE R ON THE UPWIND LEG; WHICH WE DID. AFTER THE HELI WAS ABEAM US; WE TURNED TO XWIND AND THEN TO DOWNWIND. TURNING DOWNWIND; AT TFC PATTERN ALT; WE SAW THE SMA Y AHEAD TO OUR R; NOT MORE THAN 25 FT AWAY; ALSO TURNING DOWNWIND. WE TOOK EVASIVE ACTION BY DIVING AND TURNING TO L. THE SMA Y HAD TURNED XWIND AHEAD OF ME; WHEN HE WAS TOLD TO FOLLOW ME. THE CTLR SAW THIS OCCURRENCE AND ASKED THE SMA Y IF HE HAD HIS TFC (MY SMA X). THE PLT REPLIED THAT HE HAD ME AT HIS 6 O'CLOCK POS; THE CTLR TOLD HIM THAT HE WAS SUPPOSED TO BE FOLLOWING ME; NOT AHEAD OF ME. THE SMA Y LANDED; AND TAXIED OFF TO PARK. WE ALSO LANDED; AND I TAXIED TO THE ADMINISTRATION BUILDING TO USE THE PHONE. I CALLED THE TWR AND TALKED TO THE CTLR. HE CONFIRMED THAT I 'DID EVERYTHING RIGHT;' AND THAT THE SMA Y PLT HAD ERRED BY TURNING XWIND AHEAD OF ME. I ALSO ASKED THE CTLR FOR THE ACFT'S REGISTRATION NUMBER. HE TOLD ME IT WAS XXXX. I WAS FLYING SMA X; A SINGLE ENG LAND. THE CTLR ALSO TOLD ME THAT SMA Y PARKS NEAR (FBO); AND THAT THE PLT MIGHT BE WAITING FOR ME. I FOUND THE PARKED AIRPLANE; AND SAW 3 MEN TALKING NEARBY. I APCHED THEM WITH MY STUDENT AND ASKED IF ONE OF THEM HAD BEEN FLYING THE SMA Y. ONE SAID THAT HE HAD. I ASKED HIM IF HE HAD ANY IDEA OF THE SEVERITY OF WHAT HE JUST DID. HE WAS BELLIGERENT AND ARGUMENTATIVE AT FIRST; BUT SEEMED REMORSEFUL FOR HIS ACTIONS AFTER WE HAD DISCUSSED THE MATTER. THE FACT THAT HE WAS IN A LOW WING AIRPLANE; AND I WAS IN A HIGH WING AIRPLANE; WHILE TURNING TO THE R WITH ME ON THE OUTSIDE MAY HAVE BEEN A CONTRIBUTING FACTOR AS WELL.