Resources

Reliable, vetted websites that contain a wide variety of Thinking Math Tasks (Most organized my grade and strand)

Nrich -  UK Site (Grade levels are slightly different)

YouCubed - Tasks from Jo Boaler at Stanford University 

Open Middle - Problems with multiple pathways/answers

Math Pickle - Puzzles/Problems

Inside Mathematics - Problems of the Month

MAP/MARS - Formative Assessment Lessons and Tasks by grade level (Gr 6-12)

NCTM - Problems to browse (some require membership)

3-Act Tasks - Graham Fletcher - K - 5 Tasks

3-Act Tasks - Kristen Acosta - K - 6 Tasks

3-Act Tasks - Dan Meyer - Junior/Intermediate

Tap Into Teen Minds - K-12 Tasks

Tasks from Robert Kaplinski - Search by Grade level

Illustrative Math - Search by Grade level

Yummy Math - Gr 3 - 12

Make Math Moments - K-12

Beyond the Algorithm - K-8