We've been using an app called number frames to help us strengthen our understanding of place value and begin to work together to add double digit numbers. Students work on their own to create one number and then together to add the two numbers together. Understanding of tens and ones helps children develop this skill early on. We've also been adding groups of ones and tens in a mixed way - 10, 20, 30, 31, 32, 42, 52, etc to help us develop fluency when adding not just by ones but by tens as well!
