It is not only children that should be required to have a dress code but teachers as well. I remember when I was younger all my teachers looked stern and professional. Their clothing provided us with no chance to wonder who was in charge. However, as I progressed through the school system, and definitely through college, the teachers began to look like the students in their relaxed jeans and casual sweaters. This type of attire can not continue.
If you work in the school system you need to wear clothes that are appropriate. Schools may have gotten more casual over the years but that does not mean that it is alrigh to wear casual clothing. Many schools allow their teachers to wear denim. If you wear denim then you need to make sure that you wear a dark wash denim and that the jeans fit right. The jeans should not be to loose or to tight.
You should never, ever, wear suggestive clothing. Even if you are young teacher right out of college working in the school system, wear something that is more professional. Wear a cardigan or jacket over shirts that do not have sleeves, make sure that all skirts and dresses touch the knee. Never wear shirts that are low cut and never allow your undergarments to be seen. If you are wearing something where you can see your bra strap or your bra can be seen through your top, you need to change.
Keep jewelry and makeup to a minimum. The teenagers can pile on the make up and piercings but you cannot. Wearing a necklace or bracelet is fine, but do not wear bangles up your arms or gaudy jewelry.