M.R.
Before you make any decision, go to www.wrightslaw.com and scroll down the left side of the page, click on "Retention" and read some of the articles about what happens to kids when they are retained.
If the school is saying he is "not motivated" that is code for "we should evaluate, but we don't want to." Children who struggle in the second grade are going to struggle the second time they do the same thing that did not work the first time. Get this child evaluated for processing issues, and know what could happen if you retain him.
You are right, he needs something, but you are barking up the wrong tree. If you are wrong, and it is not "maturity" you are going to cause him to loose one full year of effective intervention and teaching and if his issue is reading, you may have cooked his goose because the window of opportunity closes between age 8 and 9 to learn to read without great difficulty. You are already well into the window.
Please read about that, and what is common for kids who are the oldest in thier class once they get to high school. You won't like that either.
Good luck, you are good parents to try and help your child, but you should do a bit more research because this is no place to use "feelings."
M.
Edit: If you are just stubborn about this and are determined to do this to your son, then what you should do is write a letter to the school board agreeing to hold them harmless for the damage you are about to cause him by holding him back and excuse them from their affirmative obligation to identify his probable disablity that you are letting them igonore. Pediatricinas are not the kind of specialist you need, not by the longest shot, and in my expereince as a special education advocate, nothing is going to improve for your son by the end of his second shot at second grade with traditional teaching methods that don't work for him already. I would be willing to put money on a bet from what you just said that when you finally come to your senses and have an educational evaluation on your son, that he will have a low processing speed, deficient working memory, visual perceptual/visual motor delays, and clinical levels of attention dysfunction. How unfortunate for your boy that you will learn far too late that this was the reason he has had trouble all along. Do you get another transmission job when you need an engine?
Let me tell you, I have seen your son so many times in my career. He is 15 or 16, can barely read, could not sign his name on his drivers liscense permit, he has been held back, maybe twice, he gets some extra help, and he spends more time in the principals office than in the classroom. The school has just suggested "vocational training" and his parents just now think that maybe he is dyslexic and want him tested. They call me to help them get that testing done because schools don't usaully teach reading and writting at 15 and 16, they teach kids science and history and make them read and write about it. It is so sad, and there is very little that can be done to help that child reach the potential he so visibly had in second grade when he was held back the first time.
Do what you want to, but know what is in your future, you are making a big mistake by not doing the research, because I cannot imagine that you would choose this for your son if you had read anything about it.