Portable classrooms have been a feature of many school districts for years. From a district's perspective, the two advantages of portable classrooms are low initial cost and short time between specification and occupancy. They are intended to provide flexibility to school districts, enabling quick response to demographic changes and providing the ability to be moved from one school to another as demographics change. In reality, portable classrooms are seldom moved and become permanent fixtures of the school.  Read more about portable classrooms at www.epa.gov/iaq-schools/reference-guide-indoor-air-quality-schools#IAQRG_AppendixJ.