Which activity best fosters a 4th-grade student's skill in using mathematical language to explain why a multiplication procedure works?

• A. Solving many multiplication problems without explanation.
• B. Performing a calculation using mental math only and reporting the result.
• C. Explaining why a procedure for multiplication works using place value and properties of equations.
• D. Comparing two different multiplication strategies without justification.

Answer: (C)

Explaining why a multiplication procedure works, using place value and properties of arithmetic in clear, precise language, is what this item targets. The best activity has students justify each step of the method, showing how the parts of a number (like 20 and 3 in 23) contribute to the product and how the distributive property links those parts to the whole. For example, when computing 23 x 4, the student can say that 23 x 4 = (20 x 4) + (3 x 4) because multiplication distributes over addition, giving 80 and 12 for a total of 92. This approach ties place value to the calculation and makes the reasoning explicit, demonstrating why the method works rather than just performing it. The other activities focus more on speed, solitary result reporting, or comparing strategies without explaining the reasoning behind the procedure.