ALT OVERSHOOT DURING DEP FROM IAD; VA.

Narrative

ON AUG/FRI/00; ACR X FLT ABC; WAS AN IAD TO BOS FLT. I WAS THE PNF AND THE ONE WORKING THE RADIO. THE PF WAS THE CAPT WHO WAS ON DAY #2 OF BEING A NEW CAPT IN THE B737. HE WAS HAND FLYING THE ACFT AT THE TIME OF THE OCCURRENCE AS WE WERE MANEUVERING IN AN AREA WITH A FEW BUILD-UPS. AFTER DEPARTING RWY 30 AT IAD AND ON DEP CTL HE WAS VECTORING US 20-30 DEG HDG TO THE R AT A TIME. THE NEXT INSTRUCTION I HEARD WAS A HEADING CHANGE AND CLB TO 13000 FT. I READ BACK THE HEADING AND 13000 FT. I ENTERED 13000 FT INTO THE MCP AND THE CAPT AND I POINTED TO IT AND VERBALIZED IT AS THIS IS COMPANY SOP. AT 12100 FT THE CTLR TOLD US TO DSND IMMEDIATELY TO 10000 FT WHICH WE COMPLIED WITH. THE ONLY TFC IN THE AREA WAS AN ACR Y B737 AT 10000 FT AND 10 MI AHEAD OF US WHO HAD DEPARTED IAD AHEAD OF US. I AM UNSURE OF THE CAUSE OF THE PROB. IT COULD BE THAT WE WERE ISSUED 10000 FT AND I RESPONDED WITH 13000 FT AND THE CTLR DIDN'T CATCH IT. OR THE CTLR WANTED US AT 10000 FT AND SAID 13000 FT DURING HIS XMISSION. I DON'T REMEMBER THE ACR Y CALL SIGN. IT COULD HAVE BEEN A CLRNC FOR THEM BUT ISSUED TO US INSTEAD. OR MAYBE A NUMBER IN THEIR CALL SIGN LED ONE OF US TO SAY THE 3 IN 13000 FT. THE ONLY CONFLICT WAS PROBABLY US ENTERING THE AIRSPACE OF THE NEXT CTLR ABOVE OUR CTLR'S SECTOR. REGARDLESS OF WHO WAS AT FAULT; I KNOW I'M GOING TO BE MORE VIGILANT ON THE RADIO AND QUESTION ANYTHING THAT IS UNCLR TO ME.