Extensive research by NASA and other organizations documents the ability of interior plants to clean indoor air of toxic contaminants such as formaldehyde and benzene. Plants also help to improve humidity and reduce dust and other airborne microbe levels in today's energy efficient buildings. Studies by Washington State University and others also document the positive effects of plants on student/worker productivity and stress recovery. Adding plants to the workplace and classroom can improve student and staff health, attendance, satisfaction, and morale.
Some of the most effective air purifiers are also excellent plants for offices and classrooms due to their minimal care requirements and tolerance for office lighting conditions: Spathiphyllum (Peace Lily), Aglaonema modestum (Chinese Evergreen), Epipremnum aureum (Golden Pothos), and Chlorophytum comosum (Spider Plant).
For resources on plant research, check out the following links:
NASA Technical Reports Server (type "Wolverton" in search term)
For plant selection and care resources, check out the following links: