Well, there are 2 different issues here. The first is whether you want him to get to calculus in high school. The second is whether you want him to have a rigorous math education.
Regarding the first: in the school system I am most familiar with, the standard sequence for college-bound students is: algebra I, geometry, algebra II, pre-calculus/trig, calculus. (Advanced students can go further.) Obviously, this means that if you are going to get to calculus, you either need to (1) complete algebra I in middle school, or (2) take a summer school class, or (3) double up on math classes. If you want your son to take calculus in high school, the only options left for him are 2 or 3. So, if calculus is the goal, (2) is probably the best option.
So the question is: is calculus necessary? Unless he is pursuing engineering, etc, probably not. Some elite colleges might like to see calculus, but if his math SAT/ACT scores are good, it's not a deal breaker not to have calculus. And once you get outside the elite (say, top 20 on the USNWR list) schools, it is a total non-issue.
Now onto the second, and IMO, much more important issue: math rigor. Let me get this straight: He was in one of the more rigorous geometry classes at his school this year, but dropped it? And took Algebra I instead? And now his options are to take the more rigorous geometry class in 6 weeks over the summer or to take a watered down version of geometry as a sophomore?
If my understanding is correct, this is crap, and I would push back hard on the school on this, including climbing over the guidance counselor, to the math faculty, to the principal, to the administration, and on to the school board if necessary. Because it sounds like this school system is basically saying that kids who aren't on the advanced track at age 13 are consigned to the dust heap of math, with no opportunity to study math intensively. What could possibly be the reason for this policy? Who is it serving?
There is no good reason why he can't take the rigorous geometry class as a sophomore, and the rigorous algebra II class as a junior, etc. So he will be a year older than the other kids in the class. What possible difference could that make?