Skip counting is one concept that can help with subtracting large numbers. Counting by tens backward can help enhance the understanding of procedures for subtracting numbers with more than one digit. Using the number line to help with subtraction can also ease some of the confusion relating to regrouping. Counting backward by twos and fives can speed the process, making it less tedious and reducing the chance of errors. Skip counting is particularly helpful if the number line does not show every digit.
The concept of place value is important when subtracting large numbers, and makes it a simpler procedure. If the numbers involved have three digits, have the students count back by hundreds first, then tens, and then ones. Have them count back by thousands if there are four digits.
Estimation can also be a useful tool when subtracting large numbers. Have the students round off the numbers by whatever place value is useful before counting back for the subtraction. Rounding and estimation simplify the subtraction problem, and teaching this concept early on gives students an idea of when estimation is appropriate.
An empty number line is a strategy that does not introduce another concept, but it is still useful when subtracting large numbers. A student draws a horizontal line with a circle on the right end of it, and writes the number that is being subtracted from in the circle. The student then counts back the number that is being subtracted, making jots or other notations as he counts. Finally, he fills in the numbers below the jots that he has drawn, until he reaches the answer. If the student is subtracting a number with multiple digits, he can make larger jots for tens, hundreds and so on.