by C. Elkins, OK Math and Reading Lady

Ask your students this question: “What does the equal sign mean?” I venture many or most of them will say, “It’s where the answer goes,” or something to that effect. You will see them apply this understanding with the type of problem in which the answer blank comes after the equal sign such as in 5 + 6 = _____ or 14 – 9 = _____. This is the most common type of problem structure called **Result Unknown.** I was guilty of providing this type of equation structure a majority of the time because I didn’t know there actually were other structures, and I didn’t realize the importance of teaching students the other structures. So . . . here we go. (Be sure to look for freebies ahead.)

Teach your students the equal sign means **“the same as.”** Think of addition and subtraction problems as a balance scale: what’s on one side must be the same as the other side — to balance it evenly.

Let’s look at the equal sign’s role in solving the different addition / subtraction structures. I will be using the words **start** to represent how the problem starts, the word **change** to represent what happens to the starting amount (either added to or subtracted), and the **result. ** In this post I will be addressing the join / addition models of **Result Unknown, Change Unknown, Start Unknown and Part-Part-Whole**. I will highlight the subtraction models (Separate and Comparison) next time. Knowing these types of structures strengthens the relationship between addition and subtraction.

Three of these addition models use the term **join** because that is the action taken. There are some, then some more are joined together in an additive model. One addition model, however, is the **part-part-whole** model. In this type there is *no joining* involved – only showing that part of our objects have this attribute and the other part have a different attribute (such as color, type, size, opposites).

Helpful materials to teach and practice these strategies are bar models, part whole templates, a balance scale, and ten frames using cubes and/or two color counters. Here are 2 **free **PDF attachments. First one: Addition and Subtraction Story Structure Information. Second one is a copy of each of the 4 anchor charts shown below: Join and part-part-whole story structure anchor charts

**Join: Result Unknown**

- Example: 5 + 4 = ____; A boy had 5 marbles and his friend gave him 4 more marbles. How many marbles does the boy have now?
- Explanation: The boy
**started**with 5 marbles. There was a**change**in the story because he got 4 more. The**result**in this problem is the action of adding the two together. - Teaching and practice suggestions:
- Ask questions such as: Do we know the
**start**? (Yes, it is 5.) Do we know what**changed**? (Yes, his friend gave him more, so we add 4.) What happens when we put these together?(**Result**is 9.) - Show the problem in this order also (with result blank first instead of last) : ____ = 5 + 4
- Common questions: How many now? How many in all? How many all together? What is the sum?

- Ask questions such as: Do we know the

**Join: Change Unknown**

- Example: 5 + ____ = 9; A boy had 5 marbles. His friend gave him some more. Now he has 9 marbles. How many marbles did his friend give him? You could also call this a
**missing addend**structure. - Explanation: This problem
**starts**with 5. There is a**change**of getting some more marbles, but we don’t know how many yet. The**result**after the change is (9). It is very likely students will solve like this: 5 + 14 = 9. Why? Because they see the equal sign and a plus sign and perform that operation with the 2 numbers showing. Their answer of 14 is put in the blank because of their misunderstanding of the meaning of the equal sign. - Teaching and practice suggestions:
- Ask questions such as: Do we know the
**start**? (Yes, he started with 5 marbles.) Do we know what**changed**in the story? (Yes, his friend gave him some marbles, but we don’t know how many.) Do we know the**result**? (Yes, he ended up with 9 marbles.) So the mystery is “How many marbles did his friend give him?” - Count up from the
**start**amount to the total amount. This will give you the**change**involved in the story. - Reinforce number bonds by asking, “What goes with 5 to make 9?” or “What is the difference between 5 and 9?”

- Ask questions such as: Do we know the

**Join: Start Unknown**

- Example: ____ + 4 = 9; A boy had some marbles. His friend gave him 4 more. Now he has 9. How many did he have to start with?
- Explanation: The boy had some marbles to
**start**with, but the story does not tell us. Then there is a**change**in the story when his friend gives him some more (4). The**result**is that he has 9. - Teaching and practice suggestions:
- Ask questions such as: Do we know how many marbles the boy
**started**with? (No, the story didn’t tell us.) Do we know what**changed**in the story? (Yes, his friend have him 4 marbles.) Do we know the**result?**(Yes, he had 9 marbles at the end.) - Count up from 4 to 9.
- Reinforce knowledge of number bonds by asking, “What goes with 4 to make 9?”

- Ask questions such as: Do we know how many marbles the boy