After months of adding and subtracting with two-digit numbers, comparing two-digit numbers, and comparing three-digit numbers, not to mention skip-counting by twos, fives, tens, twenty-fives, fifties, and hundreds, we finally launched adding and subtracting three-digit numbers today.
I know what you’re thinking: “When will you teach the algorithm? It’s just easier!”
The answer: we won’t.
Because as we have done all year, we continue to create a space where students use their schema about adding and counting to generate their own new strategies. In our math workshop, our second graders compare strategies and make their own meaning, forging a stronger understanding of the math.
Building on their understanding of the open number line and place value, students fluidly made the move from making ten jumps to making hundred jumps. Phoenix quickly realized, “When you jump by tens, the ones stay the same. But look! When you jump by hundreds, the ones and tens stay the same!”Leading up to spring break, we will use our conferences and whole class debriefs to nudge students toward more efficient strategies. Soon, instead of making two one-hundred jumps, students will make a single two-hundred jump. Instead of counting on by ones with one-to-one correspondence, students will mentally add the ones.
You can continue to support your second grader at home by practicing counting forwards and backwards by tens and hundreds within 1000. Say to your second grader, “Start at 321 and keep counting by tens. 321, 331, 341….” or “Start at 925 and count backwards by hundreds. 925, 825…”