Some children struggle with subtraction right off the bat. Others find it rather intuitive until they start working with double digit numbers. Double digit subtraction often requires borrowing from one place value to add to another. This can get confusing very quickly, especially when the procedure is taught in a piecemeal, algorithmic fashion.
It is important that struggling double digit subtraction learners use base ten blocks and hundreds-tens-ones charts when working through problems. Use of these materials allows students to physically go through the trading that is involved when it is required to borrow in the subtraction process.
Be sure to thoroughly familiarize yourself with how to use the blocks and chart before attempting to use it with your child. Most sets come with instructions. Once you have learned the process, start off with simple problems (like 20-9) when working with the student. Eventually they will get the hang of how it works and will be ready to relate what they've learned to the traditional pencil and paper method.
