Noone can say for sure: too many variables (including where on the head he got hit and how much “contrecoups” or acceleration/deceleration was involved). Most concussions are fine w/time, absolutely fine Has he had imaging done? Is he doing any rehab? Rest is good. When he seems better, a neuropsych. eval. might be reassuring.
My daughter received 2 concussions in HS freshman spring and junior spring. She has been very successful the past 2 years at MIT.
No imaging. In fact, this time his pediatrician did not even feel he needed to come into the office. He said he knew his neurological exam would be fine just by how I was describing him. But he did say he needed to rest. And I think my son is doing a pretty good job of that so far. I’m much less anxious today than I was yesterday. But I will absolutely kill him if this happens again.
I had several concussions as a kid and also had an “indented skull fracture” where I knocked a chunk of my skull into my brain cavity . As far as I know I have had no lingering effects.
My D also had a concussion last year and has done extremely well since then.
My D got a major concussion her sophomore year of high school and she is now a Senior at an Ivy league school.
I personally had a serious concussion when I was about 11. I fell off the back end of a pool high dive and landed on the cement. I probably should have died. I went on to be a National Merit Scholar and had a full ride scholarship in college. I graduated and had a nice career. I’m a worrier too, so I understand where you’re coming from.
Being young makes a huge difference.
Not that I’m at all happy to hear everyone’s horror stories, but they do make me feel better knowing that you and your children all seem perfectly fine. I am a terrible worrier, and concussion is one of my huge fears. He’s been feeling absolutely fine at home for the past few days; tried school today and got a headache. 
I did not enjoy receiving that call, but I am realistic and know that we need to be patient. The good news? He’s VERY serious about his studies and getting into a good college and I really think he will be much, much more careful with his noggin from now on.
Is he sensitive to light?
No, not this time. He was with his concussion last year.
@lauriejgs I have a boy around the same age who has had 3 concussions. He seems fine now. We found that it was much, much better to work with a specialist rather than his pediatrician to help him heal properly. We did a lot of books on CD for him from the library when he couldn’t have visual stimulation.
It’s hard to say what the effects will be until your late 20s and beyond. With soccer, it’s all those tiny concussions from heading the ball. Those all add up but you wont see those affects until later. I’ve read about lacrosse and soccer players who go to top tier schools, graduate and then a few years after graduation, they go downhill.
Concussions are person dependent. Some people can get one concussion and effects will last a life time. Some people can handle more.
You probably don’t have to worry about your son’s one major concussion. But I’d worry about all those extra small ones he is getting from heading the ball. Here is a nytimes article about ball heading.
http://well.blogs.nytimes.com/2013/03/20/new-worries-about-heading-the-soccer-ball/
My brother had a concussion, from a bike fall. He graduated from Harvard magna cum laude and went on to get a Ph.D. in psychology. That said, he was NOT playing soccer.
I am a college student currently and recently suffered from a concussion.
A shelf in my dorm room fell off the wall and hit my head while I was sleeping.
The concussion was severe and I was in the hospital overnight, but after two weeks I went back to classes, was able to catch up and maintained a 3.85 GPA without help aside from meeting with my professors outside of classes to get my makeup work.
Your S will be fine 
Make him sit for a year. Been there done that. Saw 5 doctors plus MRI. Your 13 year old will get plenty of college looks at 16. S has a 4.0.
A friend’s daughter was an outstanding soccer player who probably would have gotten a scholarship. But she got a few serious concussions and ended up being homeschooled for a year because she had so many side effects and took a long time to totally recover. But she DID heal, graduated and is now at a very good university, and doing very well. She can’t play soccer any more, but her brain is fine, and that’s what counts.