There are definitely some ways to level the playing field, one can look at what other states do:
In Alabama, for example, private schools have their enrollment multiplied by 1.4 for classification purposes. Additionally, they also do classification by sport for private schools. So if a school is 3A, but their football team is deemed to be "successful" (they look at past three years state titles won and winning percentage), football will get bumped up to 4A, but other sports will remain at 3A. Two schools I can think of in SC that would be tailor made for this rule are Bishop England (Volleyball) and Gray Collegiate (Boys Basketball).
http://highschoolsports.al.com/news/art ... ol-sports/
Texas has some of the strictest policies towards private/charter schools. Texas allows private schools to join the league (UIL) only if they are not able to join another league (like SCISA, for example). Charter schools are allowed to join the UIL, but a charter school's classification will match that of the lowest classified school in nearest district, regardless of enrollment numbers. So, this would make a school like Legion at least a 4A school, regardless of number of students.
https://www.uiltexas.org/policy/members ... er-schools