Statistics

The Birthday Problem: A Short Lesson in Probability
Find out how likely it is that two people in a class have the same birthday. With an explanation of the math behind this problem and a simulation.
http://www.mste.uiuc.edu/reese/birthday/

Fact Finder Kids' Corner
The U.S. Census Bureau provides this site as part of their American FactFinder effort. The site provides facts about all of the states, in an age-appropriate format. There is a quiz, and an explanation of the Census.
http://factfinder.census.gov/home/en/kids/kids.html

NASS Kids
The National Agricultural Statistics Service provides some basic explanations of statistical terms, as well as games and puzzles.
http://www.nass.usda.gov/Education_and_Outreach/Lesson_Plans/

Percent and Probability
Learn what a percent is and how to figure probability.
http://www.mathleague.com/help/percent/percent.htm

Statistics
Article from Encarta Encyclopedia defines this branch of mathematics, offers a short history, and provides an overview of the study today.
http://encarta.msn.com/encyclopedia_761562521/Statistics.html

Using Data and Statistics
Learn about charts and graphs created from everyday examples. Also, learn to how to compute different types of average values, such as the mean or median.
http://www.mathleague.com/help/data/data.htm