E145 CREW HAD ALT OVERSHOOT IN ZAU CLASS E AIRSPACE.

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FO WAS FLYING THE ACFT. WE WERE CLRED TO CLB TO 11000 FT; WHICH I SELECTED IN ALT PRESELECTOR AND POINTED TO FO; WHICH HE ACKNOWLEDGED. THEN I WENT BACK TO MY PNF DUTIES -- SUCH AS GETTING ATIS; LNDG NUMBERS AND PLUGGING INTO FMS AND ACARS. AS I GLANCED BACK; HE WAS CLBING THROUGH 11600 FT AND I ASKED HIM TO GO BACK IMMEDIATELY TO 11000 FT. RIGHT AT THIS MOMENT; ZAU QUESTIONED ABOUT OUR ALT; WHICH WE READ BACK AND SAID BEING CORRECTED. I THINK ZAU TOLD US TO GO BACK TO AND MAINTAIN 11000 FT; WHICH WE WERE ALREADY IN THE PROCESS TO COMPLY WITH. AFTER THIS FLT CONTINUED WITH NO FURTHER INCIDENT AND LANDED NORMALLY AND SAFELY AT OUR DEST -- ORD. LESSON LEARNED IS: REGARDLESS OF HOW BUSY WE ARE ON THESE VERY SHORT 20-25 MIN SEGMENT FLTS IN THESE VERY FAST AND HIGH PERFORMANCE JET ACFT; OUR PRIMARY FOCUS SHOULD BE ON KEEPING VIGILANCE AND EYE ON FELLOW PLT FLYING AND HELPING HIM/HER TO ADHERE STRICTLY TO CLRNC LIMITS. WE WERE VERY FORTUNATE THAT SAFETY WAS NEVER JEOPARDIZED EITHER FOR OUR ACFT OR ANY OTHER TFC DURING THIS INCIDENT.