Stoichiometry: The great wall of chemistry.

   What is the most difficult concept to teach your chemistry students? During a presentation at a chemistry education fellowship, one of the discussions was about the attempting to find the 'defining concept' that chemistry students had the most difficulty with.  The consensus among the cohort of chemistry teachers was that stoichiometry was the one application of chemistry that stumped most students upon its introduction and, in some cases, became an insurmountable obstacle that could not be overcome. "I don't get it. I don't get chemistry!"
   Why is stoichiometry so difficult for students to comprehend?  I believe, like teaching all new and unfamiliar concepts, that presentation is the key to understanding. However, even the best chemistry teachers (and I do mean the best) can have problems presenting stoichiometry to students taking chemistry for the first time.
   Not all students have the aptitude or the resources to teach themselves the skill of solving stoichiometric problems. Which was apparently the old way of teaching chemistry; the kids who couldn't grasp concepts in chemistry were basically 'washed out.'
   The statement above is conjecture though, I have no data to support it.  However, from speaking with many chemistry teachers and students I got the feeling that if you didn't 'get' stoichiometry, you would basically drop the class or hope to pass by the skin of your teeth.
   Stoichiometry is a fundamental and critical part of the application and understanding of chemistry. It is essential for chemistry educators to utilize best practices in order that the majority of their students can gain the understanding and mastery of the process.