FORT WORTH — The Catholic school tour ended, and Maria Contreras felt an overwhelming desire to enroll her 7-year-old. But first, a difficult question for the principal. The second grader has trouble focusing. He doesn’t listen to teachers and runs around the classroom, she explained. Could he be expelled? More families across the country are experimenting with private school as…

Soon, half of all American schoolkids will live in states that offer public money for a private education.