At my AA WO regional the DECs we’re somewhat resented by the training department and LCAs. Only two were good enough to make through without any hiccups I’m training that I’m aware of. The others had to redo portions of training or withdrew to fly the line as an FO for a while before trying the second time. Generally it wasn’t the aircraft/systems knowledge that did them in but it was headword/SA and failing to meet the expectations of FOM and general company knowledge