Here, I was gonna re-describe the wall in the IC but I'll just do a Compare and Contrast here first.
Since you obviously aren't familiar with a compound pulley, I'll explain it out for you.
That is a compound pulley. The bottom half of the pulley is a spool of rope that is fed to the upper pulley, it is weighed down by an exchangeable amount of weight, and is held to the upper portion of the pulley by a static connector, likely rope or metal. Now. Assuming they are bound to some sort of wall and the pulley is deemed a static entity, it would take about half that of the counterweight to begin to slacken the rope. The ropes with harnesses attached at ground level would then be clipped to the ground or fastened to the ground in some way for the application of rock climbing. The angle at wich the two portions of the compound pulley are positioned make it so at more even angles, the difference between the force exerted from gravity on a 300 pound figure compared to a 120 pound figure is fractionally smaller. Thus if 220 Ib are put at the end of the bottom portion, It would take about 110 Ib to be able to pull the rope downwards. Now suppose there was rubber friction tubed on either side of the rope thus creating a resistance system, a 220 Ib weight would be able to slow the decent of someone around 300 Ib to a 10 mph descent, which is admittedly a little fast, but if you weight that much, I highly doubt you'll make it high enough to feel the fall.
I did fail to go into detail with the individual pulleys as I figured it was fairly understandable, but I'll be sure to change that up if this continues. I'll probably end up re-writing the structure of the rock climbing wall as well as solidify the fact that a school that has enough money for these kinds of expenditures would not maintain an obviously drug abusive PE teacher who makes openly perverted remarks, especially with a female principal.
I swear, there's quite a few rich kiddies attending the school you guys make out to be fit for the bottom-dwellers of the darkest ghetto in the most rundown city in China or some shit. Yes, because schools often feel like sending their students up fatal death traps even if their net-worth is greater than that of any normal school.