Education Development Center
Making Mathematics: Proof Several Different Aspects
This site is a support teacher site with numerous proof topics linked to areas of the page. A few of the topics include: What is a proof?, When Should Students Prove?, How Do We Prove?, Writing Proofs, When is a Proof Finished?,...
Cut the Knot
Cut the Knot: Proof Without Words
This site explains the method of proof using diagrams. The site gives some history of methods of proof and how it has changed through time. The site gives numerous examples of proofs without words and a practice exercise to be worked on...