World Culture Research Sites
These sites are well suited for third to sixth grades.

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National Geographic
for Kids
This is an easy to use website with information on a number of countries and their cultures.
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Time for Kids
This site has excellent information on countries and their cultures.
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Country Reports
Select a country to get 5-6 very interesting cultural tidbits about life in that culture.  You don't need to join to get access to this one feature.
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Cultures for Kids
This is a very easy site with basic information on about 11 countries.