Here are some suggested activities to teach addition of whole numbers:
1. Use base-10 blocks or bundles of sticks to model addition problems concretely. For example, show 34 + 25 by using 3 tens rods and 4 unit blocks for 34, and 2 tens rods and 5 unit blocks for 25, and combining them to show the total of 59.
2. Use place value mats or place value charts to show the addition algorithm. For example, write 34 in the tens place and 25 in the ones place of the mat, then count up to show 59.
3. Play addition war games where students flip over addition fact cards and use mental math to solve. The first to solve correctly keeps the cards.