At the regional im at. Our pass rates were excellent. They use AQP, I think most regional/contract airlines do now as well. I do know of a few that failed the checkride but passed on the second time. Just looking at the surrounding 60 guys near my hire date. A few others had training issues like what someone said above, just a slow down/extra review and then back on track. Basically, they just had a few days delay since the had the issues during training in either the clasroom or a sim session. (For example, first couple V1 cuts were unsatisfactory in Sim 1, or a poorly exectued Go around etc.) and not during a jeopardy event. (usually thats just the checkride and maneuvers validation with AQP. every airline calls them something different though) So they had to come back and redo a sim session or two before they could proceed.
From what I witnessed (im sure others witnessed differently) those guys/gals who had issues were low experienced(not time, just little IFR time and little if any turbine or Multi engine time). But not all who had that kind of experience had issues either. Many times people got delayed was due to simulator time, after one unstisfactory item. If the student had a few rough V1 cuts first time around, or a bad approach in the sim and there was no extra time left in that sim session (4 hours for two newhire FOs, approx 2 hrs each) they had to default to "incomplete" which throws a wrench in the training timeline as now you are a full sim session behind. From what I can tell, all of the 2 or 3 folks I know of with training hiccups or a checkride failure and redo, all came from VFR single engine flying. (keep in mind, everyone is different and this info is just what I witnessed) No recent time in anything as a CFII, IFR flying, ME, or turbine. Some had atp mins, some had 3000+ with 10+ years. Those with recent multi engine or turbine time, and IFR time appeared to have an easier time. Those who didnt, just appeared to have a slightly higher rate of training issues. Many VFR, single engine CFI/non CFI only guys did just fine. Just maximize your study habits with your sim partner and class mates. You will do just fine.