COMMUTER ACFT FAILS TO DSND AS ASSIGNED.

Narrative

DURING NORMAL CRUISE FLT AT 8000 FT; NEW YORK APCH INSTRUCTED US TO DSND AND MAINTAIN 6000 FT. AS THE PNF; I SELECTED 6000 FT IN THE ALT ALERTER. CALLED AND POINTED FOR 6000 FT. THE FO AGREED AND CALLED FOR A DSCNT CHK AND THE IN RANGE CHKLIST. AS PER MY DUTY AS THE PNF; I IMMEDIATELY BEGAN BOTH. WITHIN 2 MIN I HAD COMPLETED BOTH CHKLISTS AND WAS JUST BEGINNING TO RECHK OUR CURRENT STATUS WHEN NY APCH CALLED US FOR A RADIO CHK. I RESPONDED WITH A 5 BY 5. HE THEN REQUESTED OUR ALT AND I RESPONDED 8000 FT. HIS RESPONSE WAS 'I SHOW YOU AT 8000 FT AS WELL. YOU WERE INSTRUCTED TO MAINTAIN 6000 FT. DSND NOW TO 6000 FT AND EXPEDITE YOUR DSCNT.' WE DID AS INSTRUCTED AND RPTED LEVEL AT 6000 FT IN A VERY SHORT PERIOD OF TIME. AS FAR AS I AM AWARE; NO TFC WAS MOVED AS A RESULT OF OUR MAINTAINING 8000 FT. THIS WAS THE FIRST TIME THAT I HAD FLOWN WITH THIS PARTICULAR FO WHO IS IN HIS SECOND WK ON LINE. AS A RESULT I HAVE NOW BEGAN CONFIRMING THAT ONE ACTION IS AT LEAST IN PROGRESS BEFORE BEGINNING ANOTHER. I WILL ALSO NOT BEGIN ANOTHER ACTION UNLESS I CAN CONTINUALLY MONITOR THE PROGRESS OF THE INITIAL ACTION UNTIL ITS SUCCESSFUL COMPLETION. NO OTHER MENTION OF THIS WAS MADE BY ATC. OUR FLT WAS COMPLETED SUCCESSFULLY WITH NO FURTHER INCIDENTS. I FEEL AS THOUGH THIS WILL NOT OCCUR AGAIN BUT MY AWARENESS IN THE COCKPIT HAS CERTAINLY INCREASED.