No-Prep Sub Plans for Linear Functions

A math sub plan lives or dies on one question: can the students do it without the substitute teaching anything? For linear functions in grades 6–8, the answer can be a confident yes, because the ideas—constant rate of change, tables, and graphs—can be practiced from a worked example and clear steps. The lesson here needs one printed page and graph paper, and it asks nothing of the adult beyond keeping time and handing out sheets. Its content sits alongside Linear Functions, but the plan runs on its own. Drop it in your sub folder and breathe easier the next time you wake up sick.

Materials and setup

Each student needs the instruction sheet, a piece of graph paper, and a pencil. Write one anchor example on the board before you leave, or include it on the sheet: a phone plan that costs $10 plus $5 per month. That single scenario carries the whole lesson, so the substitute never has to explain a function.

The lesson, minute by minute

Give the substitute this timing and the class paces itself:

1. 0–5 min — Do-now: students read the phone-plan example and write how much it costs after 1, 2, and 3 months.
2. 5–20 min — Build a table: following the model, they make a table of months versus total cost from 0 to 6.
3. 20–35 min — Plot the points: students graph the table and use a ruler to connect the points into a straight line.
4. 35–50 min — Find the pattern: they identify the starting cost and the amount added each month, then write the rule in words.
5. 50–60 min — Exit ticket: “What does the $5 do to the graph, and what does the $10 do?”

Because every step follows from the worked example, the substitute only confirms students are moving, never explains the math.

Student-facing instructions

Print these so the class self-launches: “A linear function grows by the same amount every step. Start with the $10 fee. Add $5 for each month. Put your numbers in a table, plot them, and connect the dots with a ruler—they should form a perfectly straight line. If your line bends, check your table for a mistake.” The “straight-line self-check” is deliberate: it lets students catch their own errors without an expert present. The task self-differentiates, since early finishers can graph a second plan and compare the two lines. This reinforces the equation-building skills from Terms and Equations, keeping the day aligned to your sequence.

What comes back to you

Have the substitute collect the exit tickets and flag anyone whose line was not straight. Those tickets tell you instantly who understands that the $5 is the slope and the $10 is the starting value—the exact language of the grade 8 functions standards. It also surfaces which students still need fluency with the underlying arithmetic, such as the reasoning practiced in Fractions Complete – Grades 6 to 7, so you know precisely where to restart. One more habit pays off: ask the substitute to jot the names of any students who helped a neighbor, and any who never got their line straight. That thirty-second note tells you who is ready to peer-tutor and who needs a small-group reteach, turning a day you were absent into targeted planning for the day you return. A sub plan that returns this much information is worth keeping on file all year.

Related reading from the Teacher Hub

• Bell Ringers and Warm-Ups for Linear Functions
• Assessment Ideas for Quadratic Functions and Parabolas: Rubrics, Quizzes and Exit Tickets
• Project-Based Learning: Terms and Equations in the Real World