PLAINVIEW, Minn. — Because of black mold in a Plainville grade school, Superintendent Courtney Frie has rescheduled back-to-school activities elsewhere. Two weeks ago some carpets were found infected and cleaned. That, Frie said, was insufficient. Further tests still found elevated mold levels. A professional firm, Clean Response Restoration, was called for a thorough scrub-down. The school, with 435 pre-kindergarteners through third-graders, is at 500 West Broadway Street. The next-door high school was not affected. Nor were the district’s two other schools five miles away in Elgin.