Lesson 7: Weighted Average Inventory Method: Cost Smoothing and Financial Impact
Duration of Days: 2
Lesson Objective
Students will calculate Cost of Goods Sold and Ending Inventory using the Weighted Average method and analyze how this method smooths cost fluctuations during periods of rising prices.
• What is the Weighted Average inventory method?
• How is the average unit cost calculated?
• How does Weighted Average differ from FIFO and LIFO?
• How does inflation impact financial results under this method?
• Why might a company prefer a cost-smoothing approach?
Weighted Average Method
Average Unit Cost
Cost of Goods Sold (COGS)
Ending Inventory
Goods Available for Sale
Inflation
Perpetual System
Periodic System
Cost Flow Assumption
HS.CTE.2A – Recall and apply prior knowledge for intended purpose.
HS.CTE.2B – Pose questions and make predictions about problems.
HS.CTE.2C – Apply a solution using evidence and reasoning.
Students apply algebraic reasoning to calculate weighted averages and interpret numerical relationships. Students analyze cause-and-effect relationships between cost changes and profit outcomes.
Description: This lesson introduces the Weighted Average inventory method as a cost flow assumption that assigns an average cost per unit to both Cost of Goods Sold and Ending Inventory.
Purpose: To develop procedural accuracy in calculating weighted average while strengthening analytical comparison skills.
DOK:
DOK 1
• Define Weighted Average inventory method.
• What formula is used to calculate average unit cost?
DOK 2
• Calculate COGS using Weighted Average.
• Calculate Ending Inventory using Weighted Average.
DOK 3
• Explain why Weighted Average produces results between FIFO and LIFO during inflation.
Students connect this method to:
• Gas prices averaging over time
• Grocery price changes
• Technology components fluctuating in cost
Students may incorrectly apply different costs to different units (that’s FIFO/LIFO thinking).
• Step-by-step modeling of average calculation
• Color-coded cost accumulation
• Guided formula template
• Excel spreadsheet demonstration for automatic averaging
• Small group practice
• One-on-one reteaching
• Spanish vocabulary support for ELL students
• Guided Weighted Average practice worksheet
• Independent calculation assignment
• Comparison chart (FIFO vs LIFO vs Weighted Average)
• Exit Ticket:
“How does Weighted Average stabilize financial reporting?”
• Quiz including calculation and short analysis
Century 21 Accounting General Journal, 11th Edition
Guided Notes
Calculator
Practice Worksheet
Comparison Chart
Optional Excel modeling
Exit Ticket