Young mathematicians explore the concept of triangles as they construct altitudes of triangles to find the orthocenter. Learners construct their triangles using Cabri Jr. on their graphing calculators and find that the altitudes of a...

High schoolers investigate properties of the four centers of a triangle and explore a special property of the circumcenter and orthocenter of a triangle. This lesson requires the use of Cabri, Jr.

This site contains a comprehensive study of triangle centers. Seems more for an advanced level. Provides a list of six links to 1114 centers.