ALTDEV ALT OVERSHOT IN DSCNT MY MIL FLC.

Narrative

WE WERE DSNDING TO OUR DEST. ATC CLRED US TO CROSS 10 MI N OF WILKES BARRE AT 12000 FT. THE PNF ACKNOWLEDGED THE CLRNC AND PLACED THE ALT IN OUR REMINDER DISPLAY (WE DO NOT HAVE AN ALT ALERT SYS). THE NAVIGATOR ALSO PLACED THE ALT IN ANOTHER REMINDER DISPLAY WE HAVE AVAILABLE. THE PF ACKNOWLEDGED THE ALT. WE WERE DSNDING FROM FL200 TO 12000 FT. THE PNF (MYSELF) WAS IN THE L SEAT AND AN INSTRUCTOR PLT WAS FLYING IN THE R SEAT. IN WAS PERFORMING COPLT DUTIES (LOOKING AT A CHART FOR NAVIGATIONAL PURPOSES) WHEN ATC INSTRUCTED TO CHANGE FREQS. I PERFORMED THE FREQ CHANGE WHEN I HEARD NAVIGATOR ANNOUNCE '1000 FT TO GO' I LOOKED UP AND SAW WE WERE PASSING 11000 FT. I SAID WE WERE CLRED TO 12000 FT AND INSTRUCTED THE PF TO CLB BACK UP TO 12000 FT. HE QUICKLY CLBED BACK UP AND THEN I CALLED ATC AND TOLD THEM WE WERE LEVEL AT 12000 FT. ATC ACKNOWLEDGED. THERE WAS NO MENTION OF THE DEV BY ATC. LACK OF ATTN BY PF AND NAV. (PNF) WAS DISTRACTED BY OTHER DUTIES AND FREQ CHANGE. AN ALT ALERT SYS WOULD HAVE PREVENTED THE DEV.