I have read the stories where Jon ends up in Sunnydale or in the same
school as Harry Potter. But what if Jon ends up in the same High School
as Xander's daughter and Harry Potter. Here are the requrements.

1)How Xander is a daughter is up to you but she can not be a Slayer.
2)Harry and the daughter know each other thought magic circles.
3)Xander's daughter is good at both magic and science.
4)Jon gets along with both just fine but is a little on the wary side.
5)Harry is runing away form the Wiziarding World. (only one person
knows were he is(cannot be dumbldore))
6)Xander and daughter are not happy with the NWC.

All the rest is up to you.