Parallel geometry tasks with four levels of complexity involve students in writing and understanding proof.
Bobson Wong and Larisa Bukalov
research matters for teachers
Kristen N. Bieda and Jerilynn Lepak
Research explores how to help students build from, instead of building with, examples when justifying mathematical ideas.
Carol J. Bell
Reasoning and Proof is one of the process standards set forth in NCTM's principles and standards for school mathematics (2000).