Add and subtract whole numbers subsequence

Note that Khan Academy has adding and subtracting within 20 in 1st grade, and adding and subtracting within 100, and 1,000, in 2nd grade. That's a pretty big leap. But Khan Academy also has adding and subtracting in 3rd grade. My arrangement differs, in that I have placed this topic in 3rd grade.

• Add and subtract within 10 (kindergarten)
• Add and subtract within 20 (1st grade)
• Add and subtract within 100 (2nd grade)
• Add and subtract within 1,000 (3rd grade)
• Add and subtract beyond 1,000 (4th grade)