THE CFI RADIOED THAT HE WOULD BE CONDUCTING A SIMULATED ENGINE-OUT APRCH. 2 PLT WITNESSES, 1 OF WHOM WAS A CFI, STATED THAT ACFT WAS SEEN ON FINAL APRCH AT ABOUT 200 FT WITH THE LEFT PROP FEATHERED & THE GEAR & FLAPS DOWN. THEY STATED THAT ALTHOUGH THE ACFT WAS IN A PROPER POSITION TO SAFELY LAND, A SINGLE ENGINE GO-AROUND WAS ATTEMPTED. FULL POWER WAS APPLIED WHICH RESPONDED NORMALLY, BUT THE GEAR & FLAPS REMAINED EXTENDED FOR THE REMAINER OF THE FLT. RWY HDG WAS MAINTAINED BUT THE ACFT BEGAN SINKING & LOSING AIRSPEED. APPROX 1/4 MI FROM THE DEPARTURE END OF THE RWY & ABOUT 150 FT AGL, THE NOSE ROSE & THE ACFT ROLLED LEFT & ENTERED A SPIN OF ABOUT 1/2 TURN WITH THE NOSE DOWN ABOUT 60 DEGREES. AN ABRUPT POWER REDUCTION WAS HEARD & THE SPIN STOPPED, BUT THE ACFT STRUCK THE GROUND BEFORE RECOVERY COULD BE EFFECTED. AN EXAM OF THE ACFT & ENGS REVEALED NO EVIDENCE OF ANY PRE-IMPACT MALFUNCTION OR FAILURE.