As far as the idea that he could still be behind because look there are kids who went to school and they need remediation too, I personally don't feel that is a particularly strong or logical position. For one, the best math teaching effort of homeschooling should hopefully not be akin to the worst from public school nor should we presume learning disabilities any time a student doesn't learn something they not taught and may have devoted virtually no time to. Really, don't think we can have it both ways. If we are going to credit unschooling when kids turn out to be independent, creative, etc.when those things could have happened anyway, we need to take the lumps too.
The main reason I was motivated to post our situation here was to inform others who may be considering this path that all does not take care of itself when following this philosophy, and that not all kids are going to learn what they need when they "need" it to meet their goals. Heck, some kids may never have any goals beyond the "next level" in whatever game they are trying to master. Hopeful unschooling parents of young ones who get excited when their kids learn some simple fractions by cutting a pizza really need to hear this.
FWIW, My ds spent 2 afternoons per week this past semester in the learning center. He would then visit the teacher to go over the work he did with the tutors. He was involved in s study group as well. He has used ALEKS, as I believe that is or was required for some of his classes. He has taken the 1st semester of remedial Algebra twice, and now faces having to retake the 2nd semester. I do believe he let himself get a bit behind, and perhaps began tutoring a bit too late in the semester (I'm not sure when he began). He had gotten himself up to some "B's" on tests late in the semester, but he bombed the final (although he was very confident he had done well) and missed the "C" by 15 points.
I am quite sure that math would have never been his strong suit had he gone to school or was homeschooled more traditionally, but at least we would have had plenty of time to address issues and work a step at a time to achieve some reasonable competency. Instead it was just avoided (although I made several attempts to convince him to try it). So, I do have regrets that I did not "require" some work from him, especially in math. I feel it was my responsibility to facilitate his education, and I made the choice to unschool. That puts a lot more control in the hands of the student, but doesn't the buck ultimately stop with me when it was my decision to follow this approach in the the 1st place, even if it was my ds whose decisions about math led him to where he is today? He was a kid, he didn't know enough to ask me to work with him on math so he would be better prepared to get those requirements out of the way later on. He didn't have to do it so he didn't. I believed (hoped) he would take to math when he needed it, the way he had reading and writing. Just was not the case.