The Golden Girl

A young girl named Helena living in ancient Greece passes the demigod test, which tells whether you are allowed to go to Olympus High, where demigods train to become full fledged gods, or if you have to go to Argos Academy, the normal school. Her older sister Irene passes the test too, so she's not alone in her journey. The only problem is Irene is a real demigod, and Helena just got lucky guessing on the test.