The AdaptErrEx project, funded by the U.S. Department of Education, has developed materials to support learning of decimals through erroneous examples. The main goals are to support deeper, more robust learning and to improve error-detection skills. All the materials developed on the AdaptErrEx project will eventually be freely available through MathTutor, a website that helps middle school students learn math.

Link to Project
http://www.cs.cmu.edu/~bmclaren/projects/AdaptErrEx/