Back to school: how much net?

Type in a subject, click the mouse, and watch Google cough up thousands of Web sites in seconds.
That, teachers say, is the danger when it comes to assigning homework in the 21st century. The Internet, in some ways, has improved what students can do outside the classroom. But it’s also exposed them to an unrestrained world where sketchy sources abound and plagiarism is just a cut-and-paste away