This is an excellent, very deep drama.
Great acting and a great plot.
Even though it is set in high-school this is far from being a "Playful Kiss" kind of drama (romance is absent here), as it's definitively a thriller/legal drama, and a very good one. It's never lame and the final meaning is touching.
Probably the only flaw (but flaw it's definitively not the right term) is that I don't think it has a high rewatch value, once the mystery is unveiled.
100% recommended if you want to watch something different.