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
What this standard means
Students need to look at a scatter plot with two number variables, decide if a line makes sense, sketch a line that fits the pattern, and judge how well it fits. They are not doing formal regression yet. They are using shape, direction, and closeness to make a reasonable model.
Mastery looks like drawing a line through the middle of the data, not just connecting points, and explaining fit with evidence. Students often get stuck by forcing a line when the pattern is curved or random, drawing through the first and last point only, or ignoring outliers.
Ways to teach it
- Hands-on activity: Give pairs spaghetti sticks and printed scatter plots, then have them place a stick as a best-fit line and defend its position.
- Writing prompt: Show two possible fit lines for the same scatter plot and ask, Which line models the data better, and why?
- Quick assessment: Project one scatter plot and have students sketch a fit line, then rate the fit as strong, moderate, or weak with one reason.
- Real-world connection: Use class height and arm span data to make a scatter plot, fit a line, and discuss how close the points are.
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Related standards
- CCSS.Math.Content.HSS-ID.B.6
Represent data on two quantitative variables on a scatter plot, and describe how the variables are related.
- CCSS.Math.Content.HSS-ID.B.6c
Fit a linear function for a scatter plot that suggests a linear association.
- CCSS.Math.Content.8.SP.A.1
Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities. Describe patterns such as cl...
- CCSS.Math.Content.HSF-IF.B.4
For a function that models a relationship between two quantities, interpret key features of graphs and tables in terms of the quantities, and sketch graphs show...