Believe (2000)

After being kicked out of boarding school after boarding school, Ben is sent to live with his stern grandfather in a small town where nobody is interested in him except a girl named Katherine. The two become fast friends despite unexplained protests from Ben's grandfather and Katherine's uncle. Almost as soon as he arrives, Ben starts to see the ghost of a woman around his grandfather's house. He and Katherine want to help the ghost, who holds a connection to both of their families. As they research the past, Ben and Katherine find out that sometimes all you need to do to help someone is to believe.