Why you felt the need to post anonymously, i don't know. Anyway, here is how i approach the whole dress code issue in China

I dress as i would for any job - i.e. professionally

You are telling the students what you think of the job through your clothes.

In hot weather, i still wear formal clothes in the class-room because I am a teacher.

When teaching children i would wear less formal clothes because I am more likely to be down at their level to speak to them.

In a university, especially with the post-grad students i teach, my clothes say how serious i am about the class.

Clothes are cheap in China so don't worry about packing.

this is only a personal opinion, you have to choose how you want to be seen

'You dress, so your students will respect you!' 

You shower and shave often too, for the same reason.

Sorrel's 4th line, but I got my points!

I wear my shorts just in my private time. My shorts are so short, that I can't wear boxers under, because they are longer than my shorts. I'm 'no undies' while in shorts. Wouldn't wear them as FT in any Grade School.

I teach at a kindergarten. Normally I wear a Polo type T-Shirt. I normally wear khaki pants in winter and a nice long sleeve. In Summer,  the city I live in gets to be about 90*F or more. I will wear shorts if the weather is too hot that day. You can look professional all you want, but if you are teaching little ones and doing anything with movement wearing pants you are going to die. For college age students, most teachers here wear what you might wear when you are going out some where        semi- nice. Just plain shirt and slacks should be fine. No low V neck shirt or something too tight for a guy. For girl nothing that is too revealing.  No one expects you to show up in a suit and tie every day. You can if you want, just most teachers where I am don't.

The most casual that I get is Business Casual.

At my uni, one of our professors often wore hot pants while giving lectures. Business casual, or a simple dress shirt and dark pants were far more common though.

I usually worn chinos and business-type shirt. Something that looked reasonably professional, but without looking to intimidating (ie, formal). I want students to think they can approach me - not be put off by me!

I've occasionally worn shorts when it got really hot. I think it's ridiculous to expect teachers to sweat it out while the kids chill. However, I've also seen a lot of other crap being worn that I wouldn't.

And, sometimes, I'll wear jeans (esp in wet weather), with a good enough shirt. It can work, and still have a slightly professional air (some may disagree).

As I said,. dress well, but remember that you're giving off an impression. Some what you to act super-superior. I think there needs to be a balance between 'professional' and 'approachable'.

hoody 'n ma bling..  I'm down 4 that home-boy

I'm not a teacher, depending on your size you might not find clothes in China that fit you, and I never found clothes to be dirt cheap. A Walmart T-shirt sells for half price at home compared to China. I'm 42 reg, I can barely find shirts, jackets, bigger than that is difficult. Shoes are up to maybe size 9, I'm 11 forget it. You can buy on line but I want to know they fit before I have to send them back. Bring comfortable shoes, something with thick soles that absorb shocks and a few pairs. Chinese clothes can really suck for quality, I bought cargo shorts, they got ripped in minutes.

Theoretically, I could probably dress down as much as I damn we'll please. I see female Chinese professors wearing tight little leather mini-skirts that show every lump, crease, and bump of their asses every day that I work. They are.sbout 50, but I wonder how the 18 year old boys they teach perform in their classes. 

Realistically, if I dressed like my female Chinese colleagues, I know that I would fuel countless discussions about how laowai dress like unprofessional sluts. I usually wear business professional...it helps me get respect in my classes.

I teach at a Chinese high school and dress business casual, i.e. long sleeve oxford button down and khakis. I work in a very hot climate, so I wear tropic weight khakis and Supima cotton shirts which help keep me cool, yet still stay professional. I did not have a chance to buy new shoes when I was home in the summer, but figured I would buy them when I got back. However, none of the shoe stores in the second tier city I'm working in had my size, or the few available options looked poorly made. Consequently, I have to wear sneakers in the classroom, but I have no choice until I can make a trip to Guangzhou or Shenzhen to buy a decent pair of overpriced shoes. Definitely bring a couple pairs of shoes with you to China.

I too work in a very hot and humid environment, in Guangdong. I teach in a university and I wear shorts and short sleeved shirts most of the time. I wear mostly Nike golf shorts, or other brand golf shorts, which are actually more like cut down suit trousers than shorts. I also have tattoos on my arms which the short sleeve shirts don't cover.

I don't buy in to the 'dress like a  professional' thing. You're either professional or you're not. I am. I'm an experienced, trained professional teacher, who delivers the goods to his students, so how I dress to do that doesn't impact on their education in the least.

I wold echo the shower and shave regularly thing. As long as you're clean and presentable, you don't have to dress like a business person. You're not, you're a teacher. Teach well, and dress comfortably.