Answered By: Linda Kern Last Updated: Dec 12, 2016 Views: 820
The APA Style blog suggests we use example 30 on p.205 of the Manual for "wikipedia or other wikis". This is the only reference I can find in the manual or on APA Style. The distinctive element seems to be that a wiki is not a fixed publication and can change at any time.
Because it can change over time, the retrieval date should be included, even though example 30 does not use it (ex. 30 is from a fixed publication).
I would make two changes based on this example. Add a comma after the retrieval date, and delete the words I've marked through.
6thGradeGPS 34 SS6G11 Cultures of Europe A. (n.d.) Retrieved January 18, 2012, from the 6thGradeGPS Wiki: http://6thgradegps.wikispaces.