A resounding yes! on the screen time and structure points made above.
Also: is the workbook just too easy? How about going to the bookstore or library and having him pick out a workbook or textbook in a subject that interests him? I tried the summer workbook thing with my kids in mid-elementary school and abandoned it quickly. The work is often really boring and rote. They learned a lot more from Theo Gray's ELEMENTS (another thread discusses this) and from the DK encyclopedias they chose themselves.
