as new information becomes available. Most textbooks are out-of-date before they are even printed.

　　An interactive learning environment. Online technologies enable interaction with other students and course instructors.

　　Online learning has disadvantages too, the main one being that students work in isolation. To overcome this problem, many WBT classes incorporate features that invite student participation and collaboration including:

　　E-mail for submitting homework and communicating with the instructor and other students.

　　Message boards where students can post messages relating to class content and group activities.

　　Chat rooms, audio conferencing and videoconferencing for real-time conversation.

　　Screen-sharing, which allows students to see what an instructor demonstrates on his or her computer screen.

　　Class websites for posting of charts, graphics, links to other resources, etc.

　　Not all classes require student participation. Most use only a few of the features just discussed. Since education on demand is so new, course providers are trying to figure out what works best. And since people learn in different ways, classes vary in style. With self-paced classes, you study the course material and possibly take some online quizzes. Either no instructor is involved, or there may be a "teaching assistant" who can answer questions via e-mail. Because little human intervention is required, enrollment is open to any number of students and you can begin the course as soon as you register.

Instructor-led classes are more demanding, often requiring that you submit homework assignments, meet online periodically with other students enrolled in the class, and participate in real-time class discussions with an instructor. These types of classes generally limit enrollment (perhaps to under 50 students) and have a start and end date. Upon completion of a class you may receive a grade. Classes offered by universities typically follow this model.