Princeton School in Johnston County, N.C., is one of only five public schools in the state that contain every grade from kindergarten through 12th. But Princeton won't remain a K-12 school. Johnston County is completing a deal to buy land for a new elementary school that would siphon off the K-5 students. With them will go a way of educating that hearkens back to one-room schoolhouses and that advocates say offers a sense of community that other public schools cannot.