Unschooling or learner-centered education is not good for attaining grade school standards. I think this system works best for naturally creative-gifted kids who have mastered the 3 r's somewhat by grade 7.
If they got grade 7 math, reading and writing down and they're self-motivated, let them go. See where their genius takes them.
Only a few children are intrinsically motivated enough to control their own education without degenerating into wanting to be a pop star or beauty contest queen.
Unschooling is good for naturally intelligent kids whose families have some money and their parents, other relatives or paid caretakers/ tutors have time to guide them along but many kids are not naturally curious beyond what they're brainwashed by on TV and many are poor as well. They can't study archeology on a whim because it would cost money for books, tools, etc.