One thing that comes to mind is that EPGY covers sets (unions, intersections, etc.) in all grades (at least from 3 on - we've used 3 and are now using 5). I agree with the above - check out the scope and sequence and compare them carefully. That said, EPGY has so many exercises and the program won't let you skip what you already know. I doubt your DS would want to repeat 80% of what he's already mastered. You might be better off having him move forward and going back to fill in the gaps.