The primary difference is how you complete the assessment of learning, which is the test. For Home Study classes you complete a paper test and mail or FAX it in. For online classes, you complete the test online. Usually online classes require you to complete the class online, but this is not always required.
For example, our books are offered as both online and Home Study classes. For it to count as an online class, you register online and take the test online. (You can read the book online, but we also mail you a hard copy. For the Home Study version, we only mail you the hard copy of the book and the test.)