I went to private school for a brief time and also had extra home schooling/training, hence how i learned 3 languages by 7 years of age and to read a 4th. However I ended up going regular school afterwards. Then 'regular' school was easy. Doing algebra in private grade 3 vs just starting in grade8/9 in regular school if i recall now. Learning elements in private grade 4, then learning again grade 9/10 regular school.
Nothing wrong with it, if some parents want to educate their children better.