The Awakening (2011)

STARRING:
Rebecca Hall, Dominic West, Imelda Staunton, Lucy Cohu, Shaun Dooley, and 2 actors from upcoming season of Downton Abbey - Daniel Pirrie and Cal Macaninch

The Awakening is set in 1921, in a post-war world of loss where the bereaved seek solace in spiritualism. Haunted by the death of her fiance, Florence spends her time debunking supernatural claims, using methodical and rational explanations to disprove the notion that the dead can still haunt us. So she feels compelled to accept a request to go to Rookwood, a boarding school in the countryside where a boy has recently been found dead and rumours about a ghostly boy haunting the school are causing panic amongst pupils and parents alike. Florence sets to work immediately, laying traps and gathering scientific evidence. Gradually little secrets begin to unravel and the mystery surrounding the ghost seems to be nothing more than a schoolboy prank. As Florence is about to leave, though, she has a chilling spectral encounter which defies all of her rational beliefs and sets her on a journey toward a heartbreaking climax.

BBCFilms: official site

Thanks to Brian for mentioning film!