To cite the SGP package in publications use:

Damian W. Betebenner, Adam R. Van Iwaarden, Ben Domingue and Yi Shang (2018). SGP: Student Growth Percentiles & Percentile Growth Trajectories. (R package version 1.8-0.0) URL: sgp.io

Corresponding BibTeX entry:

  @Manual{,
    title = {{SGP}: Student Growth Percentiles \& Percentile Growth
      Trajectories.},
    author = {Damian W. Betebenner and Adam R. {Van Iwaarden} and Ben
      Domingue and Yi Shang},
    year = {2018},
    note = {R package version 1.8-0.0},
    url = {sgp.io},
  }