The purpose of sight words is to encourage fluency. So I too would encourage you to wait until he feels more confident reading before you dig too deep into sight words. If you do choose to do more down the road, we've used the mastery approach of having 7 envelopes numbered 1-6, and then one with DONE on it. As he correctly reads the word the first time and fluently, we move it up a number until it reaches DONE. My son loves this approach for the competitive aspect and that he visually gets to see his progress!