Correlation does not equal causation. Just because two events are correlated does not mean that they are causally connected. For example, if school districts with high per-student funding do better than other districts on standardized achievement tests, it does not necessarily mean that a wealthy district causes increased achievement. It could be due to other factors. Still, correlation is very helpful in educational research because correlational studies identify which variables predict or explain educational outcomes. This set of sites explores the issue of correlational research.
A sound, basic introduction to correlational research.
Includes mostly material on the correlational design.
An interactive demonstration.