Where does this fit in the unit and how long does it take?

Teach it in Unit 4 right after the money market so students can contrast the two interest-rate graphs while both are fresh. Two 50-minute periods is realistic: one to build the graph and shifters, one for crowding out, the open-economy case, and practice.

What do students need to know before this lesson?

They should be solid on supply and demand shifts from Unit 1 and on the nominal-versus-real interest rate distinction from Topic 4.2. If they just finished the money market, they are ready.

How should I grade the exit ticket quickly?

Score out of four: correct axes with the real rate on the vertical, the correct curve shifting (supply left, or demand right if they are consistent), the real rate rising, and investment falling with the term crowding out. Most misses are a mislabeled axis or shifting demand instead of supply, which are the exact FRQ errors to catch now.

Lesson plans · AP Macro Unit 4 · MACRO 4.7, MACRO 4.2, MACRO 5.5

The Loanable Funds Market and Crowding Out

Essential question: How do savers and borrowers set the real interest rate, and why does government borrowing push private investment out of the market?

2 × 50-minute periods · MACRO 4.7, MACRO 4.2, MACRO 5.5 · prints clean with Cmd/Ctrl+P

Objectives

Students will be able to draw a correctly labeled loanable funds graph with the real interest rate on the vertical axis and the quantity of loanable funds on the horizontal axis.
Students will be able to identify whether an event shifts the supply of or demand for loanable funds and predict the effect on the real interest rate and the quantity of investment.
Students will be able to trace crowding out in sequence: deficit borrowing lowers national saving, the supply of loanable funds shifts left, the real interest rate rises, and private investment falls.
Students will be able to distinguish the loanable funds market (real rate, driven by saving and borrowing) from the money market (nominal rate, set by the Fed).
Students will be able to predict the direction of international capital flows when the domestic real interest rate rises relative to the rest of the world.

Materials (all free, no student accounts needed)

Warm-up (8 min)

Project this as students walk in: a family earns $80,000, spends $65,000, and the $15,000 left over goes into a savings account or bonds. Ask where that money goes next.
Think-pair-share for 2 minutes on who supplies loanable funds and who demands them. Take two cold-call answers and steer to household and government saving on the supply side and firms borrowing to invest on the demand side.
Write the hook on the board: every dollar someone saves is a dollar someone else can borrow, and the real interest rate is the price that balances the two.

Direct instruction (30 min)

Build the graph live: real interest rate on the y-axis, quantity of loanable funds on the x-axis. Draw supply upward sloping (higher rates reward saving) and demand downward sloping (lower rates make more investment projects profitable).
Use the marginal-efficiency-of-investment example from the lesson: a project returning 8% gets funded at a 5% rate but not at a 10% rate. That is why demand slopes down.
Drill the axis label out loud: the loanable funds market sets the REAL interest rate. Put a money market graph beside it and say that graph sets the NOMINAL rate. Have students copy both labels.
List the four common shifters: national saving up or down (supply), government deficit or surplus (supply), investment tax credits or business optimism (demand), and foreign capital inflows (supply).
Introduce crowding out with the $800 billion deficit example: government borrowing uses up saving that would have funded firms, supply shifts left, the real rate climbs, and some private projects are cancelled.

Guided practice (32 min)

Project /sandbox/loanable-funds and reset to a neutral starting equilibrium so the whole class shares one baseline.
Click the 'Budget Deficit Up' control and have students predict, before it animates, what happens to the real interest rate and to investment. Cold-call one student for the rate and another for investment, then run it.
Send a volunteer to the board to shade the drop in private investment between the old and new quantity, and name it out loud as crowding out.
Reset and drag the supply curve right to model a 401(k) tax incentive that raises household saving. Cold-call: which way does the real rate move, and what happens to investment?
Run the open-economy case: tell students U.S. real rates are now above Europe's and ask whether foreign capital flows in or out, then which way that shifts supply. This is the direction students miss most.
Close with the money-market trap: put a money market graph beside the sandbox and cold-call, if the Fed buys bonds, which graph and which rate change? Confirm the Fed works the money market and the nominal rate, not this graph.

Independent practice (25 min)

Assign the 8 questions shown on /practice/loanable-funds. Circulate and flag anyone shifting demand for a government deficit, then redirect them to supply.
Send fast finishers back to /sandbox/loanable-funds to drag supply for a rise in national saving and then demand for an investment tax credit, writing one sentence each on the effect on the real rate and on investment.

Exit ticket

On an index card, draw and fully label a loanable funds graph showing a government moving from a balanced budget to a deficit.
In one sentence, state what happens to the real interest rate and to private investment, and name the effect.

Homework

Work the full 15-question loanable funds bank on /practice-test (choose the loanable funds module), including the combined deficit-plus-tax-credit item.
Read the 'Connections to Other Models' section of /macro/loanable-funds and write two sentences on how a deficit reaches net exports through the exchange rate.

Differentiation

Support: give a half-completed graph with axes pre-labeled so students focus on the shift direction, not the setup.
Support: provide a two-column sorting card (supply shifter versus demand shifter) for the four main events before students graph.
Extension: assign the combined deficit-plus-investment-tax-credit question and have students explain why the rate effect is certain while the quantity effect is ambiguous.
Extension: have students trace the full open-economy chain from deficit to net exports and present it to the class.

Misconceptions to head off

Students shift the demand for loanable funds when the government runs a deficit. Correct it: a deficit reduces national saving, so the SUPPLY of loanable funds shifts left, the real rate rises, and investment is crowded out.
Students label the vertical axis 'nominal interest rate.' Correct it: the loanable funds market determines the REAL interest rate, and the nominal rate belongs to the money market.
Students draw crowding out in the money market or bring the Fed into it. Correct it: government borrowing works through the loanable funds market and the real rate, since the Fed has not changed the money supply.
Students treat a change in the interest rate as a shift of the demand curve. Correct it: a rate change is a movement along the curve, and only non-price factors like investment tax credits shift it.

Teacher FAQ

Where does this fit in the unit and how long does it take?: Teach it in Unit 4 right after the money market so students can contrast the two interest-rate graphs while both are fresh. Two 50-minute periods is realistic: one to build the graph and shifters, one for crowding out, the open-economy case, and practice.
What do students need to know before this lesson?: They should be solid on supply and demand shifts from Unit 1 and on the nominal-versus-real interest rate distinction from Topic 4.2. If they just finished the money market, they are ready.
How should I grade the exit ticket quickly?: Score out of four: correct axes with the real rate on the vertical, the correct curve shifting (supply left, or demand right if they are consistent), the real rate rising, and investment falling with the term crowding out. Most misses are a mislabeled axis or shifting demand instead of supply, which are the exact FRQ errors to catch now.

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