Compound interest, the cost of borrowing, and a written business plan.
Ages 10–11
The one idea
Money you leave alone grows on its own — and money you borrow shrinks the same way.
Ten and eleven year olds can do the compounding arithmetic themselves, which matters: seeing the curve bend is far more convincing than being told it does.
One per pillar. Each has what to teach, a ten-minute thing to do, and the exact words you can say — so you can start right now without preparing anything.
Mowing a lawn pays once. Writing instructions that let ten people mow lawns can pay over and over. The first is a job; the second is an asset. Most people only ever build the first kind.
Do this
List three ways they could earn $50. Mark which ones stop paying the moment they stop working.
Say this
"If you got sick for a month, which of these still pays you? That's the difference that matters."
Interest earns interest. $100 at 10% becomes $110 — and next year you earn 10% on $110, not $100. It looks tiny for years, then it bends sharply upward. That bend is why starting early beats starting big.
Do this
Work out $100 at 10% for ten years, one year at a time, on paper. Do not use a shortcut — the point is watching it accelerate.
Say this
"Year one you made $10. Work out year ten. Why is that number so much bigger for the same 10%?"
A $60 pair of boots that lasts three winters is cheaper than a $25 pair that dies each year. Cost per use is the honest number, and it often points the opposite way to the price tag.
Do this
Take one thing they own and divide what it cost by the number of times they've used it.
Say this
"You've worn those about 200 times. So what did each wear actually cost you?"
If you give a fixed percentage, your giving grows automatically as you earn more, and you never have to renegotiate with yourself. People who pick a percentage early tend to keep it for life.
Do this
Pick a percentage — most people land between 5% and 10% — and apply it to every dollar for three months.
Say this
"Pick the number now, while the amounts are small. Deciding is much harder when the sums get big."
Compounding doesn't care which direction it points. Borrow $100 at 20% and you owe $120 — then interest starts running on the $120. This is exactly why unpaid debt gets away from people.
Do this
Run the same ten-year table as before, but for a $100 debt at 20%. Compare the two curves side by side.
Say this
"Same machine, opposite direction. Would you rather own it or owe it?"
An idea in your head feels finished. Written down, the gaps show up immediately — who buys it, what it costs, what could go wrong. Writing it is the cheapest way to find out an idea doesn't work.
Do this
One page, five headings: what it is, who buys it, what it costs to make, what you'll charge, what could go wrong.
Say this
"Fill in every heading. The one you can't answer is the one that would have sunk it."
8 questions. You get the reasoning either way — being wrong is where the learning is.
$100 at 10% compound interest. What's it worth after 2 years?
Why does starting early beat starting with more?
$60 boots lasting 3 years vs $25 boots lasting 1. Which costs less per year?
Which of these keeps paying if you stop working?
Why give a fixed percentage instead of whatever's left?
You borrow $100 at 20% and don't repay for 2 years. What do you owe?
What's the fastest way to find out an idea won't work?
Your plan can't answer "who buys this?" What does that mean?
Move the sliders and watch what each jar becomes. Only the Grow jar is invested, so only Grow compounds — that is the whole reason the numbers separate.
$130 a year → $1,300 after 10 years
$156 a year → $1,560 after 10 years
$52 a year → $520 after 10 years
$182 a year → $2,691 after 10 years
You put in
$5,200
You end up with
$6,071
Grew on its own
+$871
That extra $871 is money nobody worked for. It came from the Grow jar earning 7% a year on a balance that keeps getting bigger.
For parents: About $10 a week. At this level the grow jar can fund a genuine venture, which is the point of raising it.
The 7% is a rough long-run stock market average used for illustration. Real returns vary, some years are negative, and nothing here is investment advice.
Defined the way a 5th grade child would explain them — not the way a bank would.
This week's mission
They watch the curve bend with their own arithmetic, which no explanation can substitute for.
"Here's the plan, in writing, before I spend a cent."
What it costs to start
$0 to plan; set your own cap before you start
What to charge
Work backwards: pick the profit you want per sale, add your cost per unit, and that's your price.
The business lesson underneath
The gap between planned numbers and real numbers is where all the learning is. Plans are wrong; planning still pays.
The money lessons only stick if these are running underneath them.
Compounding is unconvincing as a sentence and undeniable as a graph they drew themselves. Make them plot it.
A one-page plan takes twenty minutes and routinely saves the whole budget by exposing the missing customer.
The review is worth more than the plan. Where were you wrong, and by how much? That calibration is a rare adult skill.
Tick these off through the year. If one is still open in June, that's the lesson to go back to.
Everything on this page is free and always will be. If you want structured worksheets to go alongside it, the 5th Grade packs cover the whole year across maths, reading and writing, and study skills.
Money you leave alone grows on its own — and money you borrow shrinks the same way. Concretely: calculates compound interest year by year without a formula; explains why early saving beats larger later saving; uses cost per use rather than price to compare purchases. The six lessons on this page cover each of those, and the money check tells you which ones have landed.
Around $10 a week is a reasonable starting point at ages 10–11. About $10 a week. At this level the grow jar can fund a genuine venture, which is the point of raising it. The calculator on this page lets you try different amounts and splits.
The One-Page Business: "Here's the plan, in writing, before I spend a cent." Startup cost is $0 to plan; set your own cap before you start. The gap between planned numbers and real numbers is where all the learning is. Plans are wrong; planning still pays.
Yes — all 6 lessons, the 8-question check, the vocabulary, the mission, the starter business, the allowance calculator, and the milestones are free with no signup. The 5th Grade printable packs in the shop are optional.
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