Fact Finding

Hello! I'm writing a story set in the US (FYI, I'm not an American). My main character is a high school student. My question is: if my MC is 15 when he starts high school, when should his birthday be?

For example, say the student's birthday is 26th June 1997 (this is not my MC's birthday). So what grade would this student be starting in 2012? Ninth grade or tenth grade?

I tried to search this on google but the search results vaguely say "it depends when the student was born". Very unhelpful because that's precisely what I want to know.

If this varies from state to state, then I need this information for high schools in Virginia.

Thank you.

PS: should I tag my entry or should I leave that to the mods?