We regroup or borrow in subtraction when the number we are subtracting in the units column is greater than the number of units above it. We say, "If there's more on the floor, then GO NEXT DOOR!"
In the Irish Primary Curriculum, the children in 2nd class are expected to be able to "subtract numbers without and with renaming within 99." They are also expected to be able to conduct "written calculations after plenty of practical and mental calculations."
The links to the games below may help reinforce what we are learning about in class.
Links to subtraction games
http://www.sheppardsoftware.com/mathgames/fruitshoot/fruitshoot_subtraction.htm
http://www.free-training-tutorial.com/subtraction-games.html
http://www.mathsisfun.com/numbers/subtraction-regrouping.html
http://www.softschools.com/math/subtraction/3_digit_subtraction/3_digit_subtraction_with_regrouping/
http://www.softschools.com/math/subtraction/2_digit_subtraction/2_digit_subtraction_with_regrouping/
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