How to Teach Percentages and Interest: A Step-by-Step Lesson Plan (Grades 6–8)

Percentages and interest are where middle-school math finally feels like adult life, and that is exactly why students get anxious about them. The trick is to keep the reasoning concrete and the numbers friendly at first. Here is a full lesson-plan walkthrough for one 50-minute period that carries sixth-through-eighth graders from a warm-up to an exit check without losing anyone at the decimal point.

Objectives and standards

Write two student-facing objectives on the board: (1) I can find a percent of a number using a model I can explain, and (2) I can calculate simple interest and say what each part means. These sit squarely in the Common Core ratios and proportional relationships domain for grades 6-7. The scaffolded worked examples, bar-model diagrams, and real-price task cards in Percentages and Interest – Everyday Mathematics give you consistent visuals so students see the same model every day.

Warm-up (5 minutes)

Put one question on the board: a $40 hoodie is 25% off, so what do you pay? Ask students to solve it any way they can and be ready to defend the method. You will get percent-off-then-subtract, you will get find-75%-directly, and comparing those two paths is the richest thirty seconds of the lesson.

I-do, we-do, you-do (25 minutes)

Anchor everything to a bar model so percent is always visibly out of 100.

• I do: Find 15% of $60 by drawing a bar, splitting it into ten parts of $6, and reasoning to 15%.
• We do: Together find 20% of $85, with the class directing each step while you draw.
• You do: Students find 30% of $50 and 8% of $200 on their own bar models.
• Check: One quick non-example, 120% of $40, to show percents can exceed 100.

Percent work also builds the fluency students will lean on in later courses; the same proportional reasoning shows up when they scale coordinates in The Pythagorean Theorem – Applications and when they read growth in Quadratic Functions and Parabolas, so naming that connection now pays off later.

Guided practice: simple interest (15 minutes)

Introduce I = P x r x t with a story, not a formula. A student lends a sibling $100 at 5% for one year: how much comes back? Label principal, rate, and time on the board, compute the $5 of interest, then change the time to three years and let students predict before calculating. Keep the numbers round so the structure, not the arithmetic, is the focus. Circulate and ask students to point to the P, the r, and the t in each problem they solve.

Plenary and exit check (5 minutes)

Close with a three-item exit ticket: find 20% of $35, find the simple interest on $200 at 4% for two years, and finish the sentence percent means out of ___. Sort the tickets fast as students leave. Anyone who wrote out of 10 or dropped the time factor tells you where tomorrow begins.

Differentiation and common stumbles

Keep an eye on two predictable stumbles. Some students will convert 15% to the decimal 1.5 instead of 0.15, so make the bar model the anchor they return to whenever a decimal answer looks too large. Others will find the interest but forget it adds to the principal when asked for the total owed, so distinguish interest from total explicitly on the board. For support, give struggling students friendlier percents, 10, 25, 50, so the reasoning stays visible; for a challenge, ask early finishers to work backward, if the interest was $12 on $200 in one year, what was the rate? These small moves keep every student productively busy while you circulate.

Related reading from the Teacher Hub

• 12 Hands-On Classroom Activities for Teaching Percentages and Interest
• Meaningful Homework and Independent Practice for Differentiation Rules and the Derivative Function
• Teaching The Pythagorean Theorem: Common Student Misconceptions and How to Fix Them