Column Climb above walks through adding and subtracting one column at a time, with carrying and borrowing (also called regrouping). Pick 2nd grade for 2-digit numbers, 3rd for 3-digit, 4th for 4-digit and 5th grade for decimals. If borrowing doesn’t make sense yet, Tens Treehouse shows the idea with bananas.
Carrying: when a column adds up to 10 or more, move the ten to the next column
Borrowing: when the top digit is too small, trade one from the next column
Lining up decimal points to add and subtract decimals (5th grade)
Try one together: 52 − 27 with borrowing
Ones: 2 is smaller than 7, so borrow a ten.
The 5 tens become 4 tens, and the 2 ones become 12 ones.
Ones: 12 − 7 = 5. Tens: 4 − 2 = 2.
So 52 − 27 = 25. Check: 25 + 27 = 52 ✓
Tips for parents and teachers
Always start with the ones column on the right.
Say what you’re doing: “I’m trading 1 ten for 10 ones” — not just “I borrow 1”.
Check subtraction by adding the answer back.
Matching school standards
These games line up with these Common Core State Standards for Mathematics:
2.NBT.B.7 Add and subtract within 1,000, composing and decomposing tens and hundreds.
3.NBT.A.2 Fluently add and subtract within 1,000.
4.NBT.B.4 Fluently add and subtract multi-digit whole numbers using the standard algorithm.
5.NBT.B.7 Add and subtract decimals to hundredths.
Questions parents ask
What is regrouping in math?
Regrouping is the newer name for carrying and borrowing: trading 10 ones for 1 ten (or 1 ten for 10 ones) so you can add or subtract column by column.
What grade learns regrouping?
It usually starts in 2nd grade with 2-digit numbers, grows to 3-digit numbers in 3rd grade, and becomes the standard method for multi-digit numbers in 4th grade.