Johnson, D. A. (1956). How to use field trips in mathematics. National Council of Teachers of Mathematics.
Chicago-referens (17:e uppl.)Johnson, Donovan A. How to Use Field Trips in Mathematics. Washington, D. C: National Council of Teachers of Mathematics, 1956.
MLA-referens (9:e uppl.)Johnson, Donovan A. How to Use Field Trips in Mathematics. National Council of Teachers of Mathematics, 1956.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.