AN HS25 LNDG RYY ACKNOWLEDGED A DSCNT CLRNC INTENDED FOR A BE35 AHEAD AT A LOWER ALT. THE INCORRECT READBACK WAS NOT HEARD BY THE ATL CTLR.

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BOTH ACFT WERE INBOUND TO RYY FROM THE W. I HAD BOTH ACFT ON VECTORS FOR A N DOWNWIND TO RWY 27 ILS. ACFT Y WAS AT 4000 FT. ACFT X WAS AT 5000 FT. I INSTRUCTED ACFT Y TO DSND TO 3000 FT. ACFT X READ IT BACK; WHICH I DIDN'T HEAR UNTIL THE TAPE REVIEW. I OBSERVED ACFT DSNDING THROUGH 4600 FT AND TOLD HIM TO MAINTAIN 5000 FT. HE SAID HE HAD TFC TO HIS R AND HAD HIM IN SIGHT. I INFORMED HIM THAT THE DSCNT WAS NOT FOR HIM. PLTS KNOW THEY HAVE NO ACCOUNTABILITY FOR READBACK ERRORS. THEY NEED TO BE REMINDED HOW IMPORTANT IT IS. I WORK IN A VERY BUSY FACILITY (ATL/A80) AND I HAVE SEEN MANY; MANY CTLRS GET DIALS BECAUSE PLTS MAKING READBACK ERRORS. LET'S MAKE THEM PARTLY RESPONSIBLE. MAYBE; WE SHOULD CALL ON THEM WHEN WE CATCH THEM (WHICH IS MANY TIMES EVERY DAY). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID SHE WAS VERY BUSY AND DID NOT HEAR THE INCORRECT READBACK. SHE SAID IT MIGHT HAVE TURNED OUT DIFFERENTLY IF SHE HAD USED ACFT TYPE AND FULL CALL SIGN IN HER COMS WITH THE PLTS. SHE ALSO SAID HER COM TECHNIQUE HAS IMPROVED A LOT SINCE THE INCIDENT.