Date: 201601
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Fatigue; Distraction
Second reporter function: First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi
Result: General None Reported / Taken
Contributing factors: Company Policy; Human Factors
Primary problem: Human Factors

Narrative: Pushback from Gate; leg 2; first leg involved a 0315 body clock lobby. I felt fine before push and in no way thought I was fatigued. On pushback; the gate to our immediate right commenced push before we had unhooked from the tug. We were watching them closely as we required a left 270 degree turn in order to clear them; which we did. I felt the flow on the flight deck was unhurried and normal. On taxi; we noticed that we'd not placed the transponder to TA/RA (at this point we should have expanded our SA). When I performed the throttle check; we found that the flaps were still up. We placed them to 1; completed the Before Taxi Checklist (again? for the first time?) and took off.During the climb to cruising altitude; there were a couple of minor mistakes made (switch to a new frequency and fail to check in; 10;000 feet callouts/items performed late) that indicated that both of us may not have been as sharp as we felt we were. Neither of us is certain if the Before Taxi Checklist was completed (the First Officer believes maybe; I do not remember it at all). It is possible that in our desire to not taxi into the pushback aircraft; I started to taxi without calling for the checklist. I do remember asking the First Officer to watch my wing all the way through the turn. It is also possible that I called for the checklist before the First Officer had called 'standing by flaps' and we compounded that by failure to verify the steps of the checklist.I can state without reservation that failure to put the flaps down; regardless of error trapping; is fairly egregious error. I've never done this before and feel that I am diligent in my checklist discipline. It is inexcusable regardless of the distractions encountered; but interesting (and significant) that we would both miss it simultaneously. I am relieved that the built-in error traps caught the mistake before we made it to the takeoff run up. Before today I would have thought it very unlikely that I would get caught in this particular event chain. Cheap lesson learned with nothing more than an ego hit. Having said that; and not taking any culpability off my shoulders; it is my belief that this was made possible in no small part by scheduling practices. Red-eye flying can be done safely; but requires a bit more planning and lead-in rest than we are currently devoting to it. Knowing this; it is incumbent on me to be the last link in the safety chain and be a bit more mindful when the schedule puts us at increased risk of a similar event again.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew forgot to set the flaps before taxi; but discovered the mistake during the throttle check while taxiing out. Fatigue and distractions during pushback reportedly played a role in the mistake.