Also discussed in Pprune previously was that often in the simulator during a go-around from low level on one engine (or engine failure after lift off) the PNF is so engrossed with doing things that he inadvertently forgets to call "positive rate" and in turn because the PF doesn't get the call, he too forgets to call for gear retraction and they wonder why the aeroplane isn't climbing too well. Simulator instructors have seen this enough times to realise that this is not just an aberration - it happens frequently, and is not addressed sufficiently.
The original Boeing FCTM teaching was that on observing a positive rate of climb on both IVSI and altimeter the PF calls gear up and the PNF then selects gear up after verifying. This is how it should be. Relying on the other fellow to tell you what to do is not smart thinking.