The flu is hitting some South Dakota schools hard.

Great Plains Lutheran High School in Watertown decided to cancel classes Wednesday.

Principal Bert Falak says more than 25 percent of the school's 117 students have been sick this week. He says Thursday and Friday already are scheduled off days, so the additional day off will give students an extended break to get healthy. He says a dormitory where many of the students live will be sanitized.

Last week, Rapid City schools got a thorough cleaning in hopes of reducing the number of students and staff who fall ill from swine flu. About a fifth of students were out sick at one point.

A similar cleaning was done over the three-day Native Americans' Day weekend in the Tea School District, where about 100 students were sick and missed school last week.