Once you step foot in highschool you cannot reclass but you can "PG" after higshcool
Public School, that might be true. Private school you absolutely can and they do. Or just go to public HS for a year and then re-class and repeat 9th grade in Private. 2018 from Mass on my son's team at a well known showcase started as 2016. Reclassed to 2017 and committed to UVA. Had off the field issue and commitment was broken by UVA. Reclassed again to 2018 and committed to Duke.
