What was found
IAS DISAGREE IN CLIMB AT 15K. REMAINED VISIBLE FOR <1 MINUTE. ON DESCENT THRU 14K (IN CLOUD AND LIGHT ICING) IAS DISAGREE RETURNED AND STAYED ON FOR REMAINDER OF FLIGHT. UP TO 16 KTS LOW WERE INDICATED ON F/O SIDE. CAPTAIN INDICATIONS REMAINED CLOSER TO STANDBY INDICATIONS. GROUNDED - YES. REMOVED CAPTAIN, F/O, AND ALTERNATE PITOT PROBES AND CHECKED FOR GOOD FLOW, REF AMM 34-11-01. ACCOMPLISHED PITOT FLUSHING ON ALL THREE PITOT SYSTEMS, REF AMM 34-11-00-170-801. FOUND PARTICULATE DEBRIS IN F/O'S PITOT. ACCOMPLISHED PITOT SYSTEM LEAK CHECK AND ALTERNATE PITOT PROBES, REF AMM 34-11-00.