(at around 20 mins) When Miss Cathcart is investigating the classroom where many of the ghost sightings occurred, for a brief moment on the chalkboard behind her there is a quotation that says: "They shall grow not old, as we that are left grow old." This is a line from the poem "For the Fallen" by British poet Laurence Binyon. Published in 1914, it was meant as an ode to the British soldiers dying in the First World War. This hints, among other things, at connections to the boys who were shown earlier in the film in the school photos, many of whom presumably died during the War.
Isaac Hempstead Wright (Tom Hill) and Joseph Mawle (Edward Judd, the groundskeeper) also star together in Game of Thrones (2011) as uncle and nephew. Mawle portrayed Benjen Stark, brother of Ned Stark, while Wright protrays Bran Stark, Ned Stark's son.