Step One: Introduction
Ask students to share what they know about positive and negative numbers, and discuss why they might need to use positive and negative numbers in real life. You may wish to discuss situations such as using bank accounts, spending gift cards, noting elevation on trips, adding or dropping social media connections, or studying scientific phenomena such as rising sea levels.
Step Two: Concept and Modeling
Introduce the concept of identifying and representing situations with positive and negative numbers. Begin by posting sample situations for students to discuss, and asking students to choose key words they can highlight as clues to whether the situation would be best represented by a positive or negative number.
For example, you may post the phrase “Spending a gift card on music," and ask students to note the word that helps them decide whether a positive or negative number would be appropriate (in this case, “spend" would equate with a negative number, as the balance available on the card will go down). Then, model highlighting the key word and place the word on the left side of the board to indicate that it is negative (similar to the left side of zero on a number line representing negative numbers). Take the students through one or two more examples to ensure that they understand the process.
Step Three: Sorting Exercise
Hand students some large paper to place on their desks. Ask students to fold the paper in half to demonstrate the line for zero, and make a symbol for negative (-) on the left side of the page, and a symbol for positive (+) on the right side of the page.
Students should analyze each card in the pile, highlighting key words and placing the cards on either the left or right side of the paper. Monitor students as they work and offer help as needed. Students who finish early may go to the board and write key words they highlighted on the left or right side to identify them as representing positive or negative numbers.
Special Needs or Language Learner Tip: Instead of using phrases, give students cards with key words such as “withdraw," “deposit," and so on to begin the activity. As students master the skill of identifying the key words as representing positive or negative numbers, they can begin working with phrases to identify and highlight the key words.
Assessment: After checking students’ sorted words and briefly calling students’ attention to the board to note the common words that represent positive and negative numbers, choose a method of assessment that best fits the needs of the class and works within time limits. For example, you may want to give a short quiz, ask students to spend several minutes writing in math journals to reflect on the day’s activity, or hand out a brief take-home test.
Extension: Add in the concept of zero by briefly repeating the activity as a whole class warm-up, introducing cards with neutral phrases such as “sea level," “zero balance," “debt paid," etc.