Getting Started 
Misconception/Error The student does not understand how to locate a line of good fit. 
Examples of Student Work at this Level Rather than locating the line to minimize the distances between the line and the data points, the student draws:
 A line above or below most of the data points.
 A line that appears to intersect several data points but is not a good fit for the data.
 A nonlinear curve that connects some or all of the data points.

Questions Eliciting Thinking How did you decide where to draw the line?
How well does your line fit the data points?
What makes a line a good fit for data? 
Instructional Implications Explain to the student that the line of fit models the pattern in the data. If the scatter plot is roughly linear, then it is justifiable to model the relationship between the variables with a line. Explain that there are mathematical techniques for locating the line, so the distance between the data points and the line is minimized. When informally fitting a line to the data, the objective is to place the line as close to as many data points as possible. Guide the student to redraw the line, so it better fits the data. Then ask the student to write its equation.
Show the student other scatter plots (e.g., ones with a strong positive, strong negative, weak positive, weak negative, and no linear relationship) and model a line of good fit. Explain to the student why the line is (or is not) a good fit for the data. Provide another set of scatter plots and encourage the student to draw a line that fits each set of data. Assist the student in assessing how well his or her lines fit the data.
Consider implementing the MFAS tasks Line of Good Fit  1Â and Line of Good Fit  2Â (8.SP.1.2). 
Moving Forward 
Misconception/Error The student is unable to write the equation of the line of fit. 
Examples of Student Work at this Level The student draws a line of good fit but is unable to write its equation. The student:
 Identifies two points on the line and attempts to calculate the slope but is unable to do so correctly.
 Chooses two data points on the graph rather than points on the line of fit to use in his or her calculations.
 Indicates that he or she does not know how to write the equation.

Questions Eliciting Thinking How do you write the equation of a line given its graph?
What are the two important parameters of a linear function? 
Instructional Implications Review as needed:
 Linear models and lines of best fit.
 Slope and yintercept.
 Linear functions written in slopeintercept form, y = mx + b.Â
 Pointslope form of the equation of a line.
Guide the student to identify the coordinates of two points on his or her line and to use the coordinates to find the slope of the line. Then ask the student to use the slope and one of the points to write the equation. Provide feedback.
Provide additional opportunities to write equations of lines. Consider implementing the MFAS tasks Writing a Function From Ordered Pairs, The Cost of Water, or Functions From Graphs (F.LE.1.2). 
Almost There 
Misconception/Error The student makes an error in using the equation to make a prediction. 
Examples of Student Work at this Level The student draws a line of good fit and correctly writes its equation but when predicting the price of a 3000 square foot house, the student:
 Uses the line or the scatter plot (rather than the equation) to estimate a predicted value.
 Makes a computational error when solving for the predicted value.

Questions Eliciting Thinking How did you determine your prediction? Did you use the equation?
I think you made a mistake in your work. Can you find it? 
Instructional Implications Provide feedback to the student regarding any error made and allow the student to revise his or her work. Ask the student to use the equation to make other predictions about the cost of a house given its area. 
Got It 
Misconception/Error The student provides complete and correct responses to all components of the task. 
Examples of Student Work at this Level The student draws an appropriate line of good fit and correctly writes its equation (e.g., the student writes the equation yÂ = 0.07xÂ + 60). The student correctly uses the equation to predict the value of a 3000 square foot house, for example, as $270,000.
Note: The student may initially give a predicted value such as $250 but immediately corrects upon questioning. 
Questions Eliciting Thinking How could you find the line of best fit?
Are there other models beside the linear model that seem appropriate? 
Instructional Implications Have the student explain the meaning of the slope and yintercept in the context of the linear model.
Consider implementing other MFAS tasks aligned to standard SID.2.6. 