1. National Science Teachers Association. An NSTA Position Statement: Learning Science in Informal Environments.http://www.nsta.org/about/positions/informal.aspx(accessed Sep 2017) .
2. National Science Foundation. Advancing Informal STEM Learning (AISL): Research on Learning in Formal and Informal Settings.https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=504793(accessed Sep 2017) .