The Classical Learning Test looks promising but is still very, very young.

STAA's present policy concerning the CLT is that it is considered an elective test.  Students pursuing an STAA diploma still need to take two other more widely accepted standardized tests during high school (such as the PSAT, ACT, SAT, CAT, Stanford, or TerraNova).  

By special petition, STAA will accept just the CLT passing results along with a copy of university acceptance paperwork that shows the student was accepted and is in the middle of making financial arrangements to attend the university.