The Cookie Cart: A Paired Lab in Unit Conversion and Unit Rates

Grandma Pearl’s Cookie Cart: Paired Learning Lab

A paired-learning lab in unit rates and unit conversion · Grades 6 and 7 · About two class periods

Grandma Pearl’s chocolate chip cookies sell out every Saturday. Then her mixer breaks. A new one costs $380, and two kids decide to fix that by starting a cookie cart. A neighbor lends them the $380, they pool $200 of savings, Grandma sets the price at 50 cents a cookie, and the clock starts: three months to fill the jar to $1,000, repay the loan, and get their savings back.

There’s one problem on day one. Grandma’s recipe card says cups and teaspoons. The store sells flour by the pound, eggs by the dozen and vanilla by the fluid ounce. Before your students can buy a single bag, they have to translate the recipe, cost a batch, decide how many batches their money will stretch to, and shop in whole bags with leftovers to track. Then they do it again in Month 2 and Month 3, with a bigger jar and a stocked pantry each time.

Built for pairs, not just groups

This is a paired lab. Every team has exactly two students with fixed roles for the whole lab: the Pantry Buyer owns flour, sugars and oats; the Dairy & Mix-ins Buyer owns butter, chocolate chips, eggs and vanilla. Each paired worksheet has two links. Each student works their own four ingredients, the team worksheet combines the halves, and neither partner can finish alone. Both halves use the same math, so the work is equal and each student’s contribution is visible to you.

• Teams are created automatically when you release the lab. Mark absentees, let the platform build pairs (one trio for odd numbers), drag to rearrange, release.
• Students meet their partner in the app, propose a team name, and you approve it. That name goes on the leaderboard at the end.
• Partners check each other’s rows and both sign off before a month’s numbers lock. Accountability is built into the worksheet, not left to you.
• Carry-forward is real: Month 2 can only be solved with Month 1’s numbers, so accuracy matters to students without you having to say so.

The math

• Convert measurement units with ratio reasoning: cups and teaspoons to pounds, dozens and fluid ounces (6.RP.A.3d)
• Unit rates and unit pricing: price per pound, cost per batch, cents per cookie (6.RP.A.3b, 7.RP.A.1)
• Decimal operations with money, rounded to the cent, every month (6.NS.B.3)
• Rounding up in context: the supplier sells whole 5 lb and 10 lb bags, and the combined bill must stay under budget
• Subtraction with carry-forward: bought minus used gives the pantry, and the pantry reduces next month’s shopping list

One core idea, used three months in a row, until it’s routine.

How it runs

• Short story decks that students read on their own screens set up each problem and keep them inside the narrative. No spoilers, no worked answers on the slides.
• Interactive, auto-graded worksheets with immediate feedback. Students compute and enter; the engine checks.
• Live teacher dashboard: who started, who finished, who’s stuck, by team and by partner.
• You present two things: the opening story deck on Day 1 (five minutes) and the leaderboard at the end. Everything in between runs itself.
• Calculators allowed. The work is in setting up the right calculation, not in long division.
• Nothing to print. One device per student and a projector.

What’s included

• 4 sections, about two class periods: Introduction (team, roles, conversion, batch cost), then Month 1, Month 2, Month 3 and the final count
• 13 student story decks, 11 interactive worksheets (paired and team), a teacher overview deck, and a full Teacher Guide with learning objectives, step-by-step instructions and answer keys for every worksheet

Prerequisites

Students should be able to multiply and divide decimals (with a calculator), work with money to the cent, and read “per” language. No prior unit-conversion experience is needed; the lab teaches it with a worked example before students touch their own ingredients.

Why teachers pick it

Pair work usually fails on logistics: who’s with whom, what happens when someone’s absent, how to tell who did the work. This lab handles all three inside the platform, and wraps the math in a story students want to finish. By Month 3 they’re converting, costing and counting without being told to, because Grandma is waiting for her cookies.