You can use Writing with Ease (WWE) in a couple of ways.
The hardcover text covers all four levels of WWE, and if you want to generate your own curriculum (the dictation, copywork, and so on), this text is all you need.
If, however, you want to have the prep work (the dictation, copywork, and so on) done for you, you can purchase the Workbook, which provides both teacher guidance and the student material, and you need not purchase the hardcover text.
That said, the hardcover text includes reference- and trouble-shooting material beyond what is included in the workbooks, so it can be a useful resource.