To cite package 'SGP' in publications use:

Damian W. Betebenner, Adam Van Iwaarden and Ben Domingue (2012). SGP: An R Package for the Calculation and Visualization of Student Growth Percentiles & Percentile Growth Trajectories. (R package version 0.9-0.0. URL http://cran.r-project.org/web/packages/SGP/index.html

Corresponding BibTeX entry:

  @Manual{,
    title = {{SGP}: An R Package for the Calculation and Visualization
      of Student Growth Percentiles \& Percentile Growth
      Trajectories.},
    author = {Damian W. Betebenner and Adam {Van Iwaarden} and Ben
      Domingue},
    year = {2012},
    note = {R package version 0.9-0.0},
    url = {http://cran.r-project.org/web/packages/SGP/index.html},
  }