Under United States copyright law, no copyright notice is required in order to have copyright protection on your original work. This is the statement from the United States Copyright Office about when your works are protected: 'Your work is under copyright protection the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device.' This means that you do not need to have the copyright statement on your webpage in order for your webpage to have copyright protection.
Placing the copyright statement on your webpage does give you several additional rights. For example, if you have the copyright statement on your website and someone were to violate your Copyright, that person could not defend the violation by claiming that s/he was not aware the website was copyrighted.
Further protections can be gained by actually registering your copyright with the United States Copyright Office, such as the ability to bring suit against someone who violates your copyright. This is probably a bit beyond what is necessary for a teacher webpage, though.
You can find a lot of good information about Copyright on the United States Copyright Office website at www.copyright.gov. The section titled "About Copyright" on the main page provides useful information.