As first grade teachers, we lay an important mathematical foundation for understanding 2-digit addition with and without regrouping. Developing number sense and understanding place value is a huge factor for students to be successful with these concepts. Students should be proficient with understanding basic addition and building 2-digit numbers with base ten blocks before teaching this concept.
As I think back to being a kid, I don’t ever remember talking about place value. When adding 2-digit numbers, I learned how to “carry”, but I never really understood the “why”. I had never seen a base ten block until I was in college learning to teach. Using base ten blocks is so important as we begin to teach 2-digit addition. Our students deserve the time to properly develop this mathematical foundation.
Model 2 Digit Addition – I Do
Typically, early 2-digit addition is taught in the spring of first grade. Adding a 2-digit number and a multiple of 10 is a great place to start! This guarantees that students will not need to regroup when adding.
Start by modeling 2-digit addition without regrouping for students. Here’s a few tips:
- Use actual base ten blocks to model, you can transition to digital manipulatives over time.
- Use two colors of blocks. Build the first number in one color, and the multiple of 10 in a second color. This will help students see the two separate numbers.
- Use a Base Ten Mat to keep your work organized.
- Go slowly and explain what you are doing and why for each step.
- Show addition problems in both a vertical and horizontal format.
2 Digit Addition Guided Practice – We Do
Once you have modeled several problems for students. Distribute place value mats and base ten blocks to students. Make sure they have 2 colors of tens. Display an addition problem such as 52+30 for students to build with place value blocks. Then, have students count all of the blocks to find the sum is 82.
Another option is to use a two-row base ten mat, this mat provides more scaffolding. With this mat, students build the 2-digit number on the top row, and the multiple of ten on the second row. Then, they combine the numbers. This mat is a great option if you don’t have 2 colors of base ten blocks or if students are struggling with the simpler mat. It also works great for partner games where students take turns building one of the numbers.
Transitioning to a Representational Model
Once students have a solid grasp using base ten blocks. You can transition to using a representational model. Activities like digital slides with moveable manipulatives, drawing quick pictures, and worksheets are great options to use for instruction and practice.
Digital activities, with moveable pieces, are a fun way to teach this skill! Use this activity together on your interactive board or assign to students to complete.
Worksheets are a great option for independent practice and to assess student mastery of skills.
Two Digit Addition on a Hundred Chart
A hundred chart can be another great option for adding a multiple of ten to a 2-digit number. Before using this strategy, students need to know how to quickly navigate the chart. They need to understand that moving down one row is the same as adding ten. If you’ve already completed a unit on 10 more and 10 less, you likely practiced that skill on a hundred chart.
Model for students how to move down multiple rows to quickly add multiples of 10. If we have 52+30, we can start at 52 and move down 3 rows to add 30. Some students might need to count 10, 20, 30, as they navigate down the rows. I recommend using a see-through manipulative for this activity.
You can find this activity on TPT or in the First Grade Math Hub.
