Thanks for the replies everyone. I am going to try some of these suggestions this week and see if things improve.
I am also going to try to tap into his creative side and see if that helps. The worksheet that he did without trouble involved him creating story with the pictures. This wasn't part of the instructions, just something he did on his own. I think I will try using this week's pictures as a scavenger hunt list. See if he can find other pictures to match in his own books or the actual objects in our house. Then see if he'll color them to match. Or just see if I can get him to make up another story.