Your soil looks a little heavy. You could cut it half and half with perlite or gravel. Something bigger than 1/16" (or 1.5 mm if your a metric person) and will not absorb water. You want it so that it will not hold water but be a little damp. if it stays muddy that will likely kill it.

What kind of drainage do you have in that tub? None, or little drainage will kill your plant.

What time frame are you talking about? These can be very slow growing plants for a while and then burst with new growth.

I would not bother misting it. Others might advise it.

Another option is to wash all the soil off of it and grow it hydroponically (semi-hydro) in water. If that sounds interesting to you ask and I'll explain it.

Plenty of material there to survive.

Stop misting. It does absolutely no good (as far as humidity is concerned).

It needs drainage. The potting mix is too heavy, indeed, although these plants tolerate bad mixes better than other plants. I'd re-pot pronto, using a quality mix.

Josh

Yeah, I agree with the others.
It looks like the plant is getting too much water. These plants like really good drainage, and don't like their roots to be wet (unless grown hydroponically ÃÂ la dellis326...? That's something I hadn't tried before, but it sounds interesting).

You can improve the drainage of the soil by mixing it 1:1 with orchid bark chips (you can buy them at nurseries and hardware stores). That's what I do for my monstera.
Also make sure there are plenty of drainage holes at the bottom of the tub.

Just to add to the conversation. You brought in a sickly monstera to start with, it can take a while for damage to show so what is happening may still be a result of the treatment at the school. That's the risk you run with rescued plants (although its all the sweeter if they make it). Best of luck!