S.W.
I have a daughter going into 4th grade. In 1st grade, she was tested way below "grade level" for reading. The teacher told us, in front of her, that she wasn't a good reader :-/ At the end of 3rd grade she tested in the 99th percentile for reading!!
There was no magic involved. Children's brains develop at different rates. Read the book "Nurtureshock" for much more info on this. She did get Title I help at school during 1st grade and that did help. Her father and I read to her every day. I modeled reading to her, and stayed positive and encouraging, but didn't force OR bribe.
The most important thing is for you to help him enjoy books. Read to him every day, this will help his comprehension, also. Chose books above his reading level to read to him, to increase his vocabulary. I would suggest stopping the treats and rewards right now for doing something that should be, and likely will be eventually, done for enjoyment and as a reward unto itself.