Two Digit Addition Strategies

In second grade, students are expected to solve two digit addition and subtraction problems. This week, we have been focusing on adding up to four two-digit numbers using place value and properties of addition.  So what exactly does that mean?

• Place value strategies: Splitting a number into tens and ones (decomposing) and adding the tens together, the ones together, and then adding your two sums to get your total.  In later grades, this is called partial sums.  Many of you have seen this strategy on our Educreations.

• Properties of addition: We use the commutative and associative properties of addition (though not by name,) to decide what order to add two or more numbers.  We worked on many addition shortcuts at the beginning of the year, so when adding the numbers  

6 + 4 + 6

students might decide to add 6 + 4 first, because those are making ten pairs, OR add 6 + 6 first, because those are doubles students should have memorized.  This freedom allows students to answer problems more quickly by avoiding math facts that are more difficult.

Take a look at our recent Educreations to see how we are doing solving four two-digit addition problems.  One of the biggest obstacles students face is not solving a multi-step addition problem, but getting their basic math facts right!

Problem Solving

In math, we have been working on solving addition and subtraction stories that include two digit addition or subtraction.  This is extra tricky, because the problems require reading skills, critical thinking skills (as we decide what kind of math is needed, and what the "unknown" is,) and our math skills!  We know lots of ways to solve two digit addition problems, and are working on learning two digit subtraction problems.  We recorded our thinking in our Math Journals.

Exemplars

Each week, we become mathematicians-in-training and explore expert problem solving strategies through our Exemplars.  Exemplars are really tricky math problems, which require math reasoning and thinking, as well as collaboration, to solve.

Each week, we introduce a problem and highlight one of the math strategies that successful mathematicians use to complete difficult tasks.  By the end of the year, we should be adept at using all of these strategies.  The problem solving strategies which we are learning to use, called the Math Practices in our Common Core Math Standards, are:
1. Make sense of the problem, then persevere
2. Use math that makes sense
3. Prove and defend our answers
4. Show our thinking in different ways
5. Use math tools to solve
6.  Explain my thinking using math words
7.  Notice patterns to help solve
8. Use a strategy that you've used before

The practices in blue are ones we have learned and practiced in class so far this year.  The ultimate goal is for students to be comfortable facing challenging mathematical tasks, and have a toolkit of strategies they can fall back on.  They also should be comfortable taking risks in small group settings, sharing their ideas and not focusing only on the "right" answer.  Our focus is on the process, rather than the product.

Check out some great pictures of our class using math tools and patterns to help solve an exemplar called Betty's Blocks.

Hundred Grid Clues

Today we practiced using our Hundred Grids in class to solve addition and subtraction problems.  We realized that when you add or subtract one, you move to the left or the right.  When you add or subtract ten, you move up or down the column.

We used these rules to play Hundred Grid Clues together.  This would be an easy game to play with each other at home too!

We took turns giving clues one the hundred grid.

Hundred grid clue prompts.

Math Fact Practice

This week in math we began focusing on learning addition facts.  As second graders, we are responsible for mastering our basic addition facts (up through 20).  This means that we should be able to answer them within 3 seconds.  The goal is to have them memorized have a trick to figure them out very quickly.  

To make mastering these facts more interesting, we have been learning games to help us practice.  Ask your child to teach you how to play Domino Pull, Plus One/Plus Two Go Fish, Beat the Calculator, or Plus One/Plus Two Concentration at home!

This week we are focusing only on our plus one, plus two facts.  Check out our class in action!

Domino Pull is a game where students flip over a domino from a pile.
If they flip over a plus one or plus two fact, they get to keep it,
and write the addition sentence on their board.

Writing addition sentences is another important skill this
game practices.

Students loved playing this- and it helped us learn our facts.