A B737-800's flaps and slats did not extend during approach; the crew did not recognized the no flap condition until flaps 15 was selected with no flap gauge movement. An emergency was declared; the leading edge devices only extended and an emergency landing completed.

Narrative

During approach; flaps and LEDs (leading edge devices) did not extend. [I] got local vectors to complete QRH. Alternate flap Extension Procedure resulted in LEDs full extend; trailing edge flaps indicated up. First Officer confirmed that configuration visually from cabin. Completed Trailing Edge Flaps Up QRH and landed uneventfully. Declared emergency and requested emergency equipment standby and follow to gate. I made three PA's and briefed the A Flight Attendant while he was in cockpit during First Officer trip to cabin to inspect; and the Flight Attendants did excellent job calming passengers. I was pilot flying and called for flaps; but did not check gauge to see if we were getting the selected flap. As pilot not flying; I try to check it (but sometimes I don't; I suppose). I can't remember if it was after calling for flaps 5 or gear down and flap 15; but I looked at the gauge to see a zero flap indication. Apparently the First Officer was not checking. After a short moment of disbelief; I announced the observation to the First Officer. I think he had a moment of disbelief also until we looked at the airspeed. We were below maneuver speed for clean but did not get a stick shaker. We immediately disconnected autopilot and corrected speed and went around. Moral: if you select something; make sure you get it!