Complex sentence: After the 2011-2012 school year, Manteno Elementary School is building a massive addition to the school after compelted, this will house Pre-K and Kindergarten and 1st grade.
Split into simpler sentences: After the 2011-2012 school year, Manteno Elementary School is building a massive addition to the school. After it is completed, this will house Pre-K and Kindergarten and 1st grade.