Beyond the Board

Hiraeth was born a medium. She made friends with ghosts, people who died long ago. They told her that heaven did exist, but they weren't allowed inside. Most of them had been trapped on earth for so long they had forgotten who they were. Hiraeth's only live friends were Lotus, a believer in spirits and things beyond, and Syd, a witch.
After being expelled, Hiraeth's gut tells her to go back to the high school. The three girls prepare everything for a seance and sneak into the building in the dead of night. They use motion activation devices and a spirit box to communicate with the ghosts. A few teenagers in the bathrooms, a few children from the twentieth century, and something more sinister.