The state of Texas awards an A-F score to public and charter schools, as well as the charter school providers and school districts. The ratings are based on STAAR scores; college, career, or military readiness; graduation rates; and grade completion rates. Charter Schools: Charter schools are tuition-free, open-enrollment public schools that differ from public schools in a few ways. For instance, they are often allowed to be more flexible, and they operate under a nonprofit status. Depending on how competitive they are, some charter schools may also offer enrollment on a lottery basis.