Christine Schutt’s latest is set at an elite UES private school (like the one she teaches at), but bucks any comparisons to Gossip Girl. Astra Dell, a Waspish, beautiful senior, contracts a rare disease at the start of the school year and casts a kind of lugubrious pall over her fellow classmates and teachers. Her plight, set against the strivings and shenanigans of her friends and family, proves the puffy prep-school genre can shoulder real emotional weight — and that indeed, it sometimes should.