Add the concept of a number line to your lesson plans. A number line has a "0" in the middle with positive numbers to the right and negative numbers to the left.
Show students how to add and subtract integers using the number line. For example, to add 5 + 5, you would start at the five, count to the left five numbers to end on 10, which is the correct answer.
Incorporate negative numbers into the problems, which are also integers. For example, to add 5 + (-5), you would start at 5 on the number line again and then count backward 5 spaces, since you're actually adding negative five spaces in the problem. This brings you to 0, which is the answer to the problem.
Go over the rules for adding and subtracting negative and positive numbers once this concept is introduced using the number line. The main rule is that a "+" and "-" next to each other can be made into a "-" symbol. For example, "5 + (-5)" would become "5 -- 5," which is "0" -- the same answer that was determined when completing the problem using the number line.
Introduce rules for multiplying and dividing negative and positive integers to your fourth-grade students. For example, when multiplying a negative integer times a negative, the answer equals a positive integer. When multiplying negative integer times a positive, the answer is a negative integer. For division problems, these rules can be reversed.
Ask your students to do some problems on their own after each integer operation is introduced. A worksheet works well for this process, as does allowing your students to work with partners. Be sure to walk around the room and be available for questions. It can be challenging to fourth-grade students to keep the rules straight.