Oooh, oooh, I know... there was JUST a talk on the School about this.
Adam did not observe the Sabbath
And Jesus was the end of the law and made it obsolete, including the Sabbath
So, no Sabbath required
The end.
Seriously, though... if he really wants to know, ask him to look at the ORIGINAL commands for the Sabbath and what it was to be for. I WISH we had a sabbath today since it was to be a day of "complete rest". Many religions make it out to be a day of worship, but that wasn't what God had commanded. I just did a word study on this, and I'm not done with it. By "word study", I mean that I searched for every occurrence of "sabbath" in the Bible and have all the verses in a document. I'm reading through it. This gives the sense of what is behind a certain word. For "sabbath", thus far, I can only gather that it was meant to be no working, resting, giving animals a much needed break. There wasn't any sense of going to worship on that day. The Israelites weren't even permitted to light a fire in their homes that day. The point was to rest.
Don't know if this helps at all.