C172 WAS ON SHORT FINAL INTO UNCONTROLLED ARPT WHEN ANOTHER ACFT TOOK THE RWY AND DEPARTED. GAR WAS EXECUTED AND EVASIVE ACTION TAKEN TO AVOID THE OTHER CLIMBING ACFT.

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A NEAR COLLISION ENSUED NEAR THE BLUE ASH ARPT; ISZ. THE PROB AROSE AS 2 ACFT WERE PERFORMING PRACTICE TKOFS AND LNDGS; A 3RD WAS WAITING TO DEPART; AND A 4TH WAS INBOUND FOR FULL STOP LNDG. THE ACFT WAITING TO DEPART CUT OFF THE 4TH ACFT WHICH WAS ON SHORT FINAL. MYSELF AND A STUDENT WERE IN THE 4TH ACFT. THE CROWDED TFC PATTERN WAS DISCOVERED AS WE OVERFLEW THE FIELD 2000 FT AGL AND WITNESSED THE FIRST 2 ACFT; BOTH C172'S PERFORMING PRACTICE TKOFS AND LNDGS IN CLOSE PROX; LESS THAN 1/2 NM APART. #1 COMPLETED A TOUCH AND GO LNDG AND #2 PERFORMED A GAR; PRESUMABLY BECAUSE #1 HAD NOT CLRED THE RWY. WE CONTINUED PAST THE ARPT TO CIRCLE AROUND AND ENTER THE PATTERN ON A 45 DEG ANGLE FOR THE DOWNWIND. #1 AND #2 BOTH JOINED THE DOWNWIND AS WE CONTINUED ON A 45 DEG ANGLE. WE NOTICED THE 2 CESSNAS ON DOWNWIND WERE CLOSE TO EACH OTHER; SO WE SLOWED AIRSPD TO ALLOW MORE SEPARATION. WE HEARD THE CITABRIA HOLDING SHORT ENQUIRE A 5TH ACFT THAT HAD JUST DEPARTED IF THEY WERE 'GOING TO GET A HOTDOG.' THIS XMISSION STEPPED ON #1'S XMISSION FOR TURN TO BASE. #1 XMITTED THE TURN TO FINAL; AND THE CITABRIA HOLDING SHORT WAS HEARD XMITTING 'ARE YOU GUYS EVER GOING TO LET US DEPART?' #2 TURNED AND RPTED BASE LEG AS WE JOINED DOWNWIND AND MADE OUR POS RPT. AS WE APCHED OUR TURN TO BASE; WE NOTED #2 ON FINAL WAS LESS THAN 1/2 NM BEHIND #1 WHO WAS TOUCHING DOWN. WE PROCEEDED TO TURN BASE TO FINAL AND SAW #1 OVER THE DEP END OF THE RWY; #2 OVER MIDFIELD ON A GAR; AND THE CITABRIA TAKING THE RWY. MY STUDENT MADE A CALL TURNING FINAL; AND THE CITABRIA XMITTED; 'CITABRIA; WE GOING TO DEPART NOW; BECAUSE; YEAH.' IT SEEMED THE CITABRIA NOTICED US ON SHORT FINAL AND CHOSE TO DEPART ANYWAY. MY STUDENT ANNOUNCED A GAR AND TOLD THE DEPARTING CITABRIA THAT WE WERE ON THEIR L. THE CITABRIA CONTINUED TO CLB AND HEAD SLIGHTLY L INTO OUR FLT PATH; STILL SLIGHTLY LOWER. I TOOK CTLS FROM THE STUDENT AND HEADED R AND OVER THE RWY TO AVOID THE CITABRIA; WHICH WAS NOW ABOUT 200 FT L AND AHEAD. THE CESSNAS WERE TURNING DOWNWIND AND XWIND; RESPECTIVELY. AS WE APCHED ABEAM THE CITABRIA; IT BEGAN A CLBING TURN TO THE R CLOSE TO OUR FLT PATH AND ANNOUNCED DEPARTING PATTERN TO THE N. I QUICKLY DSNDED AND HELD COURSE EXTENDING UPWIND LEG. I XMITTED 'ACFT DEPARTING N; SOMEHOW YOU SLIPPED TO OUR L. WE ARE DSNDING UPWIND SO YOU WILL CLB OVER US.' THE CITABRIA NEVER CONFIRMED THEY HAD US IN SIGHT; BUT INSTEAD MADE A COMMENT ABOUT HOW BUSY THE PATTERN WAS. I WATCHED THE CITABRIA CLB OVER US THROUGH THE SKYLIGHT WINDOWS. IT WAS ABOUT 100 FT ABOVE US. WE DEPARTED THE PATTERN AND REENTERED AFTER WE HAD CLRED THE AREA. I BELIEVE THE CITABRIA'S IMPATIENCE WAS A CONTRIBUTING HUMAN FACTOR. THE ONLY ACTION TO PREVENT A RECURRENCE IS TO URGE PLTS NOT TO TAKE CHANCES. GIVEN THE RADIO CALL THE CITABRIA MADE WHEN DEPARTING; I BELIEVE THE CITABRIA CLRED THE AREA AND SAW OUR ACFT ON FINAL; AND DECIDED TO DEPART ANYWAY.