What state are you in? Did your son go through common core math or just traditional in private school? Many states have scrapped common core (or partially scrapped the math part) in favor of traditional math. And part of the reason is Algebra. Some states with common core have changed Algebra to 9th grade only. Too many kids failing. Some schools don’t make it to calculus and others have changed it to making a combination year of geometry and Alg 2 in 10th to make up the difference. From what I read (I’m no expert–we thankfully didn’t go through this and our state scrapped it anyway) the “immaturity” they speak of (and yes, I’ve read that term several times) doesn’t mean your kid is necessarily immature socially but that the concepts can be “too mature” at this age (hence the Algebra waiting until 9th grade). Good teachers often teach both but “showing work” in common core is frustrating to someone who can “do math in their head” (very convoluted to a sane brain in my opinion) but that is where the grade lies.