2008 "Extreme" Number Sense Resources
Articles
"Teaching to Develop Students as Learners" by Debra I. Johanning and Teri Keusch
"A Vision for School Mathematics," Principles and Standards for School Mathematics, NCTM, 2000
"Number and Operations and Algebra," NCTM Curriculum Focal Points
Powerpoint Presentations
Developing Number Sense Concepts Across K-12 (pdf file of slides)
Problems and worksheets
Estimating percents on a circle graph
Estimating exercises (sums, products, quotients)
Hundred-pound, x-legged Phoenix lander
The sum of two 5-digit numbers is less than 100 ...
And then there were those Adopted Numbers...