How did you celebrate your high school graduation? Wimberley’s Sarah Jarosz marked the occasion with a debut album, Song Up in Her Head (Sugar Hill). The eighteen-year-old overachiever has been well-known regionally for years, appearing at numerous festivals and even with the Austin Symphony. Yet unlike a lot of child prodigies (she started playing mandolin at age ten), she’s no mere technical instrumentalist: She’s also a strong singer. Her soulful voice provides the glue for her longish, melancholy compositions, and she’s brimming with big ideas—almost too many, in fact. Overlong and a bit unfocused, Song Up in Her Head , which was recorded in Nashville around her class schedule, is nonetheless surprisingly accomplished. It’s easy to see why bluegrass stars like Jerry Douglas, Abigail Washburn, and Tim O’Brien are converts. Free-flowing, meditative songs like “Tell Me True,” “Long Journey,” “I Can’t Love You Now,” and “Left Home” (written by someone who has yet to do so) betray an informed confidence and aged spirit. And her cover of the Decemberists’ “Shankill Butchers” is inspired both in concept and execution.