Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
Add and subtract within 100 using abstract methods. See POW #8: Four Square Sum on this page for a puzzle involving a bit of logic and adding multiple 1-digit numbers to a sum within 100. Hopefully this puzzle is fun for your students. They should be able to solve it quite easily.
Have your students play this game. Then lead this investigation. Watch this to learn how. After students have found a couple blotches, get them to notice the numbers must add to the total number of squares in the grid. Then have students do this activity, but replace the three questions with the following: Which numbers between 4 and 35 can you make, and for each number that you can make, in how many ways can you make it? Conclude by leading this investigation. Watch this and this to learn how.