1. Agustini, IP, Tomi, A., & Sudjana, IN (2016). Playing Method of Physical Education Students in Learning Class III III C SDN Krian Sidoarjo. Physical education.
2. Bjorklund, DF, & Brown, RD (1998). Physical play and cognitive development: Integrating activity, cognition, and education. Child Development. https://doi.org/10.1111/j.1467-8624.1998.tb06229.x
3. Burdette, HL, & Whitaker, RC (2005). Resurrecting Free Play in Young Children. Archives of Pediatrics & Adolescent Medicine. https://doi.org/10.1001/archpedi.159.1.46.
4. Burghardt, GM, 2011. Defining and recognizing the play. In: Pellegrini, AD (Ed.), Handbook TheOxford of the Development of Play. Oxford University Press, New York, pp. 9-18.
5. Bishop, JC, Curtis, M., 2001.Introduction.In: Bishop, JC, Curtis, M. (Eds.), PlayTodayin the Primary School Play Ground. Open University Press, Buckingham, PH, pp.37–57.