2-Digit Mental Mathematics

Strand: Number
Outcomes: 6 and 7

Step 3: Plan for Instruction

Guiding Questions

What learning opportunities and experiences should I provide to promote learning of the outcomes and permit students to demonstrate their learning?
What teaching strategies and resources should I use?
How will I meet the diverse learning needs of my students?

A. Assessing Prior Knowledge and Skills

Before introducing new material, consider ways to assess and build on students' knowledge and skills related to mental computation of 2-digit numbers. For example:

Take 10 minutes at the beginning of mathematics lessons to do mental mathematics. Have students work on addition and subtraction questions involving 1- and 2- digit numbers. Ask them to figure out answers without using pencil and paper, and to keep their answers to themselves until most of the class has an answer. Write down all the answers students come up with. Ask them how they figured out the answer and write that down. Check to see if students understand the approaches used by their peers.
To see if students are able to use doubles for addition and subtraction to 18, ask them to solve 12 – 6 or 6 + 8.
To see if students are able to use a making tens strategy for addition and subtraction to 18, ask them to solve 9 + 7 or 7 + 4.
To see if students are able to build on a known double for addition and subtraction to 18, ask them to solve 7 + 8.
To see if students are able to use addition to subtract, ask them to solve 17 – 13.

If a student appears to have difficulty with these tasks, consider further individual assessment, such as a structured interview, to determine the student's level of skill and understanding. See Sample Structured Interview: Assessing Prior Knowledge and Skills .

B. Choosing Instructional Strategies

Consider the following guidelines for teaching about mental computation of 2-digit numbers:

Use an "Assessment for Learning" approach to ensure that students understand the learning intentions for all activities, understand what distinguishes appropriate strategies, receive descriptive feedback about their progress and have opportunities for self and peer assessment. For example, use the "Traffic Lights" for 2-digit mental computation master found at the end of this document. Have students use this tool for self-assessment of learning intentions both before and after learning about mental computation of 2-digit numbers.
Teach mental mathematics in short 10-minute minilessons to help students develop particular mental mathematics strategies that might be useful in the problem-solving lessons and investigations that follow. Suggest to students that they might find mental mathematics strategies helpful when problem solving. Help students develop particular strategies by asking planned questions that encourage the use of the strategy and increase in difficulty and sophistication.
In problem-solving situations, accept strategies that show less sophistication, such as counting on and counting back. If students are ready, encourage them to try more abstract strategies. Mental mathematics strategies are naturally differentiated so that students can successfully arrive at an accurate answer with a strategy that makes sense to them. This activity helps struggling students move toward more fluency in partitioning and manipulating numbers and parts of numbers. This fluency develops over time and through experience, leading to greater mathematical understanding, efficiency and abstraction.
Ensure that there is adequate time for students to share and compare mental mathematics strategies with the rest of the class. During this time, ask if other students understand and can explain the strategy or use it to answer a similar question. Discuss the relative efficiency of particular responses in particular situations. Some strategies are equally efficient in some situations. Efficiency also depends on the level of understanding of the person using the strategy.
Consider teaching mental computation throughout the year, and highlighting strategies in problem-solving contexts where they are useful, so that students, who may not have thought of using them to solve a problem, can appreciate their effectiveness.
Use games that reinforce mental mathematics strategies.

C. Choosing Learning Activities

Learning Activities are examples of activities that could be used to develop student understanding of the concepts identified in Step 1.

Sample Learning Activities
Adding Left to Right	Download Activities
Going to the Nearest Ten	Download Activities
Thinking of Addition	Download Activities
Using Doubles	Download Activities