I'm here with math questions again.

From the beginning, my son (now 8yo) has not been able to truly grasp place value. Since coming to adding with carrying, we have hit that wall again. I decided to spend yesterday and today showing him each problem in the textbook, and workbook with the MUS blocks (base 10 rods) with him simply watching me. I wrote every step out on the whiteboard for him to follow. Today he copied me on his whiteboard. He taps out and loses focus after about 4-5 problems.
It doesn't seem to me that the lightbulb has gone on in this area yet. We've hit major bumps before and by slowing down and redoing the hands on activites he seems to catch on eventually. My plan tomorrow is to go back to the +1, -1, +10, -10 activities and redo those so he can better grasp adding tens.
My question is, how slow do we go? I hate to progress to subtraction when he can't even comprehend the addition. But you Singapore pros might have a different perspective than me. I ordered the 2a/2b books already and it looks like we will be moving on to numbers within the 100s and I know he hasn't figured out the 10s yet. Any advice?
Thank you!
sara