Rimrock Water Plant Filter Sand: A Grade 3 Kilograms Lesson

Hook (5 min): Pass around a sealed 100-gram object and a 1-kilogram object without telling students their masses. Ask each student to hold both and say which one a scale would give the bigger number for. Record a quick show of hands, then reveal both masses and leave the question open for now.

Direct instruction (10 min): Put the two objects on the balance side by side and write "100 grams" and "1 kilogram" on the board beneath them. Explain that a kilogram is a much larger unit than a gram, so it takes a very small number of kilograms to name a heavy object. Introduce the setting: at Rimrock Water Plant, sand for the filters arrives in bags, and the crew records every bag in kilograms because the bags are far too heavy to describe in grams. Model one problem aloud, thinking through the operation before computing: two bags of 20 kilograms each is 2 groups of 20, so the crew records 40 kilograms.

Guided practice (10 min): Work handout items 1 and 2 together as a class. For each item, have students name the operation before anyone computes, and write the equation on the board with a letter for the unknown. Ask two students to defend the operation choice in their own words. This is the formative check: at least four out of five students should name the correct operation for item 2 before the class moves on, and if fewer do, repeat the modeling with one more subtraction problem of your own.

Independent practice (15 min): Students complete handout items 3 through 6 on their own. Circulate and look for students who write kilograms where the problem gives grams, which is the most common recording error at this stage.

Closure (5 min): Students answer handout item 7 as an exit ticket and hand it in on the way out. Sort the exit tickets into two piles as you collect them so that tomorrow's warm-up can target the students who multiplied incorrectly.