In this lesson, students deepen their conceptual understanding of subtraction within 1,000. They model decompositions with place-value disks on their place-value charts while simultaneously recording these changes in the vertical form. Students draw a magnifying glass around the minuend and ask familiar questions: Do I have enough ones to subtract? Do I have enough tens? When the answer is no, students exchange one of the larger units for 10 of the smaller units. They record the change using the algorithm, following this procedure for each place on the place -value chart.