Teacher Guide to Addition and Subtraction
Learning addition and subtraction is easier than you may think. Whether you know it or not, you already know how. In fact, you knew how to add and subtract before you knew the words for numbers. For example, you know that, if you have three cookies in your lunch and your friend Jill has only two cookies, you have one more cookie than she does. Likewise, you know that, if you have three cookies, your friend Ron has none, and you give him one, you now only have two cookies. Addition and subtraction is the same thing. The only difference is that the rest of the story is missing, so, instead of you having cookies in front of you, all you have is the numbers themselves. There are several ways you can improve your math skills: 

Counting
The easiest way to learn how to add and subtract is to count it out. Use your fingers and toes, a bowl of dry beans, toy blocks, or anything that you have around. To practice adding, count the number of blocks, for instance, of the first number and set those aside. Next, count out the second number and add those to your first pile. To get your sum, count all the blocks you have set aside.
Learning to subtract is just as easy. Begin by counting out the larger number of blocks. Next, take away the second number. Lastly, count the remaining blocks to get your answer.
Using a Reference Number
The hardest part about counting is knowing what to do if you do not have enough items to count. When this happens, you need to "lock" the biggest number in your head, then start counting on your fingers, or whatever else you have available, from there. For example, if you are adding 9 + 7, you would start by "locking" the number 9 in your head and then using your fingers to count out the rest.
Make A Ladder
You can also break your problem down into parts by drawing a ladder. For example,
if you are subtracting 12  7, draw a ladder with 7 and 12 marked and then
draw a step between them  say 10. You can then figure out the difference
between steps, in this case
10  7 = 3 and
12  10 = 2.
Next, add 3 + 2 (it equals 5)  so, the answer to 12  7 is 5.
Play Games
For practice with addition and subtraction, try playing numberbase games, such as Yahtzee or Uno. In each of these games you keep score by adding and subtracting. In addition to games you play with friends, you can always ask your teacher or parent to help you find these types of games online.
Tell a Story
Sometimes, addition and subtraction are easiest when you are able to tell
a story with the numbers. For example, if your teacher assigns you a problem,
like 3 + 2, you can find the answer by asking yourself a question like,
"If I have three video games and I get two for my birthday, how many video
games would I have?"