Many times I have observed in simulator training the PM anticipating calling "positive rate" when his altimeter hasn't moved and always the PF then calls "gear up" as a reflex. Monkey see - monkey do, syndrome.
Not a trainer myself, but that is one of the things that is a constant pain in the behind. PFs calling "gear up" before the PM calls "positive climb" and most are in a big hurry to get the gear up.
I was tought from the start of my career in a jet to check for three things before calling positive climb: baro altimeter counting up, radio altimeter doing the same and IVSI positively indicating a climb. Some just see the horizon dropping and think they are climbing when in fact they are simply rotating. The end result is someone putting the gear up while still on the ground, see for example the luxair case in Saarbrücken. Or putting the gear up in a go around before an actual sustained positive rate is achieved.