SMA INSTRUCTOR AND STUDENT HAD A FORCED; OFF ARPT LNDG WHILE PRACTICING FORCED LNDGS.

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AT ABOUT XA45; I WAS CONDUCTING A VFR TRAINING FLT. AT 6000 FT MSL I GAVE THE STUDENT A STANDARD PROCEDURE SIMULATED ENGINE OUT. AT APPROX 200 FT AGL; LNDG ASSURED I ASKED THE STUDENT TO RECOVER THE ACFT. UPON APPLYING FULL PWR THE ENGINE BEGAN SPUTTERING AND RAN VERY ROUGH; NOT DEVELOPING FULL PWR. I VERBALLY ANNOUNCED CTL OF THE ACFT AND VERIFIED FULL THROTTLE AND PLACED THE CARBURETOR HEAT ON; AT THIS POINT IN TIME THE ACFT HAD DESCENDED THROUGH 50 FT AGL AND WAS STILL SPUTTERING AND DEVELOPING 50 PERCENT PWR AT BEST. IT WAS APPARENT THAT THE ACFT WAS GOING TO TOUCH DOWN. I PERFORMED A SOFT FIELD LNDG AND UPON TOUCHDOWN THE ACFT IMMEDIATELY BOGGED DOWN ON THE SOFT MUD; AND CAME TO A STOP. I IMMEDIATELY SECURED THE ACFT AND CALLED FOR ASSISTANCE ON MY CELL PHONE. EVEN THOUGH I WAS COM WITH ARTCC; IT WAS MY JUDGEMENT AND BELIEF THAT THERE WAS NO NEED TO DECLARE A PRECAUTIONARY OR AN EMERGENCY SIT. IN ORDER TO PREVENT A RECURRENCE OF THIS SIT I WILL ENSURE THAT CARB HEAT IS ON AND OCCASIONALLY CLR THE ENGINE BY MOMENTARILY INCREASING THE RPM DURING SIMULATED ENGINE OUT; BEST GLIDE PORTION OF THE PROC.