To cite package 'SGP' in publications use:

Damian W. Betebenner, Adam VanIwaarden, Ben Domingue and Yi Shang (2016). SGP: Student Growth Percentiles & Percentile Growth Trajectories. (R package version 1.5-0.0) URL: sgp.io

Corresponding BibTeX entry:

  @Manual{,
    title = {{SGP}: Student Growth Percentiles \& Percentile Growth
      Trajectories.},
    author = {Damian W. Betebenner and Adam {VanIwaarden} and Ben
      Domingue and Yi Shang},
    year = {2016},
    note = {R package version 1.5-0.0},
    url = {sgp.io},
  }