CCSS.Math.Content.8.SP.A.2
The Standard
Know that straight lines are widely used to model relationships between two quantitative variables. For scatter plots that suggest a linear association, informally fit a straight line, and informally assess the model fit by judging the closeness of the data points to the line.
Common Core State Standards for Mathematics · Statistics and Probability
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students look for a roughly straight pattern in a scatter plot and draw a line that represents the trend. They judge how well the line fits by checking how close the points are to it.
What Mastery Looks Like
- Students draw a reasonable line through the center of a roughly linear scatter plot. They explain the fit by noting the distance of points from the line and the balance of points above and below it.
Common Misconceptions
- Students may connect the points instead of drawing one line through the middle of the data. They may force the line through the origin or ignore whether points are balanced above and below it. Some judge fit by the slope rather than by how close the points are to the line.
How to Assess It
- Give students a scatter plot and ask them to draw a line of fit, then rate the fit as strong, moderate, or weak using point closeness as evidence.
Lesson moves
Ways to Teach It
Plot paired arm span and height measurements on grid paper, then use string to place a line through the center of the points.
Write: Why is your line a reasonable model, and which points make the fit weaker?
Play Line of Fit Match: pair scatter plots with candidate lines, then defend each choice using closeness and balance above and below.
Compare hours of sleep with reaction time data, fit a line, and explain whether the model supports a useful prediction.
Free download
Printable 8.SP.A.2 Worksheet
A ready-to-print activity worksheet aligned to CCSS.Math.Content.8.SP.A.2, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
Download the worksheetLearning progression
Where This Standard Sits
See the whole path on the Statistics & Probability progression map.
Before This Standard
If students are struggling here, check these first.
- CCSS.Math.Content.8.SP.A.1
Students must first read scatter plots and recognize linear association before they can fit and judge a straight-line model.
- CCSS.Math.Content.7.RP.A.2a
Recognizing straight-line relationships on coordinate graphs supports seeing linear patterns in scatter plots, though statistical fit is a new idea.
- CCSS.Math.Content.8.EE.B.5
Understanding slope and straight-line graphs for proportional relationships helps students interpret and draw informal linear models on scatter plots.
What This Unlocks
Mastery here sets students up for these next.
- CCSS.Math.Content.8.SP.A.3
Informally fitting a line helps students see what the model represents before using its equation, slope, and intercept in context.
- CCSS.Math.Content.HSS-ID.B.6a
Informally fitting and judging linear models prepares students to fit functions to data and use them for contextual predictions.
- CCSS.Math.Content.HSS-ID.B.6c
Students need to see when a scatter plot is roughly linear and choose a line before writing that line as a function.
- CCSS.Math.Content.HSS-ID.B.6
Informal line fitting and judging closeness prepares students to describe form, direction, and strength in high school scatter plots.
- CCSS.Math.Content.HSS-ID.C.8
Informal judging of linear fit and point closeness prepares students to interpret correlation as strength and direction of linear association.
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