A CPR FLT CLBS 800 FT ABOVE ITS ASSIGNED ALT WHEN THE CAPT MISINTERPS THAT CTLR'S PHRASEOLOGY AS A CLRNC FOR A HIGHER ALT 20 NM W OF MSL; AL.

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ACFT WAS CLRED TO 12000 FT MSL. OUT OF 11000 FT; ZME ISSUED TFC AT 12 O'CLOCK POS AND 10 MI. CTR ADVISED IF WE COULD TAKE A TURN TO THE R OR SIGHT THE TFC; WE COULD CONTINUE THE CLB. WE ACCEPTED THE TURN TO THE R. WHEN THE CAPT SIGHTED THE TFC; CTR RADIO WAS TOO BUSY TO ADVISE HIM. HOWEVER; THE CAPT THOUGHT WE WERE CLRED TO A HIGHER ALT AND HAD CONTINUED TO CLB. THE ACFT CLBED TO 12900 FT BEFORE DSNDING BACK TO 12000 FT. BEFORE REACHING 12000 FT; CTR GAVE US A HIGHER ALT. PROBABLY 2 THINGS COULD HAVE BEEN DONE TO PREVENT THIS FROM HAPPENING: 1) CREW SHOULD MONITOR CLB CLOSELY THE LAST 1000 FT. 2) USE THE AUTOMATION SYS. THE CAPT WAS HAND FLYING THE ACFT AT THE TIME. SUPPLEMENTAL INFO FROM ACN 475879: I TURNED R; GOING THROUGH 11000 FT AND HAD TFC IN SIGHT AT THE SAME TIME. FO RPTED 11000 FT FOR 12000 FT. I WAS PROGRAMMED FOR HIGHER OR TO KEEP CLBING. AT 12000 FT; I LOOKED AT ALT IN PRESET WINDOW; ASKED FO WHAT ALT WE WERE CLRED TO -- AT TIME WE WERE 12500 FT. FO SAID WE WEREN'T CLRED HIGHER. CLB WAS STOPPED AND A DSCNT WAS STARTED. AS MISTAKES LIKE THESE OCCUR; I WISH I KNEW THE ANSWER. ONE FACTOR WAS FIRST TIME TO FLY WITH THIS PERSON AS FO. I GUESS TO PREVENT THIS IS TO FLY WITH REGULAR PEOPLE OR IF SOMEONE NEW; BE EXTRA CAREFUL.