Scatter Plots and Lines of Best Fit
I can judge a line of best fit, write its equation from two points on it, and predict with it.
What students learn
Students learn to describe the association in a scatter plot, judge a line of best fit by balance, write its equation from two points on the line, and predict inside the data.
See inside
The key rule
About as many dots lie above a line of best fit as below it, and it follows the trend. How many it touches is not the test.
slope = rise ÷ run, on the line
Use two points ON the drawn line, where it crosses grid corners, not two data dots.
Watch out
For the 8 dots in the graph above, a student picks y = x + 2 as the line of best fit because it passes through 3 of them.
The mistake: 3 dots on the line, so it fits bestTouching dots is not the test.
The fix: the other 5: 1 above, 4 belowNot balanced, so not a line of best fit.
The mistakes it targets
- Picks the line that touches the most dots
- Uses run over rise for the slope
- Loses the sign of a negative slope
- Calls a prediction outside the data interpolation
- Draws the line through the two end points
- Reads b as a point's y-value when x is not 0
The interactive Teacher Deck (33 slides, PowerPoint)
- The Learn page taught on screen: 9 fill-in blanks, each filled on its own click as students write it
- The worked example one slide per step (five steps), each with the reason for the step
- Six practice and three apply problems: a your-turn slide with a think-time bar, then the solution one line per click
- Jump buttons on every slide: go straight to any problem, the answer bank or the exit ticket
- Speaker notes on each problem: the question to ask, the worked answer and the common error to listen for
- A completed deck PDF (19 pages) with every slide fully built, to print or post
The student packet (9 pages)
- Learn: guided notes with four definitions, the key rule, a worked example and a Watch Out error pair
- Practice: two warm-up, two standard and two stretch problems, with an answer bank for self-checking that hides three common-mistake decoys
- Apply: one word problem, a reasoning prompt and one error analysis
- Assess: an exit ticket of four items, two per page, with an I-can self-rating
- Homework (page 5): eight new problems, two warm-up, four standard and two stretch
- Answer key (pages 6–7): every problem worked step by step, six common mistakes with what to do about each, and a grading guide, plus the homework key (page 8)
- Color and ink-saver editions of the whole packet
Standard codes refer to the Common Core State Standards for Mathematics. Math Class 678 is an independent publisher, not affiliated with, sponsored by, or endorsed by NGA Center or CCSSO. Every product is sold on Teachers Pay Teachers.