@jshaving I was enlisted in the crayon eaters division (USMC) and being able to do pull-ups/chin-ups equated to higher likelihood of being promoted…
Where this matters is that the physical standards for women changed partially through my enlistment and the ladies suddenly had to perform pull-ups where it was not required before. What most of them found success with was starting off with a “flexed arm hang” which effectively means having them stand on a chair so they can be in the “up” position, and remove the chair so they can try holding that position for as long as possible. They would typically do this 3-5x per ‘session’ and it got most of them to a point of being able to at least perform a pull-up/chin-up.
Another method for the men was to integrate some thick bands to reduce resistance - allowing for higher reps (the men were required to do 20 pull-ups while women were required to do 7, because ‘equality’). Most of us had sticking points somewhere around 12-15 reps but the bands allowed us to gain muscular endurance - and most ended up reaching 20 full bodyweight pull ups.
Finally, you could always have them use one of the assisted pull-up machines and increase intensity.
None of this has any bearing on ‘training’ whatsoever, simply information/experience I had from my crayon eater days.