Overcrowding in my school means that nobody has his or her own classroom. Some teachers (me, I will admit) are fortunate enough to have classrooms to themselves for more than 50% of the day, but no one has a room that she and only she occupies 100% of the day. This, as you can imagine, makes it harder to do classroom maintenance and decoration, since you can't exactly hang posters and change bulletin boards and schlep furniture while one of your colleagues is trying valiantly to maintain the attention of 30+ recalcitrant teenagers.
Also, some teachers are traveling to 3 and 4 classrooms a day, sometimes back-to-back-to-back. Imagine squeezing your way through a crush of students laden with a work basket, a textbook, your planbook, maybe your purse or your laptop bag, and the packets and handouts for the day. Then, you have 2 minutes to get wherever it is you're going, position yourself by the door, and start the lesson on time. Good luck with all that.
As well, if your school has built a decent reputation for itself on (among other things) smallish class sizes, that's going out the window. There are very few classes in my school under 30 anymore, and rooms that were not designed to hold 30+ almost-adult bodies are bursting at the seams. Students are sweating even in air-conditioned rooms with the lights off (I'd hate to see, and smell, the non-air-conditioned schools).
I should mention that I work with consummate professionals who are dealing with all this as gracefully as possible, as well as an administration that is reasonable and forgiving and knows that the situation can't generally be helped. We are also lucky in the supplies department; due to whatever magic my principal was able to work with the budget, so far there hasn't been a real shortage of anything, and broken copiers and computers are being fixed promptly. But again, we are very lucky. Some schools certainly are not.
"This is what austerity looks like," Michael Mulgrew pointed out in the Daily News article. He's certainly right on this one.
What does overcrowding look (and smell) like at your school?