Last steps

Compute the average

Sum	Average
0.0	NaN

Compute the Upper Control Limit

Simply compute the standard deviation and multiply by 3 and add to the average:

Compute the Lower Control Limit

Simply compute the standard deviation and multiply by 3 and subtract from the average:

For the lines, you have the data necessary to plot the chart.

Very last step

The percent of students getting a Free or Reduced Price Meal comes from the following sources:

Percent
Data source