To cite the SGP package in publications use:

Betebenner DW, Van Iwaarden AR, Domingue B, Shang Y (2020). SGP: Student Growth Percentiles \& Percentile Growth Trajectories.. R package version 1.9-5.0, https://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 = {2020},
    note = {R package version 1.9-5.0},
    url = {https://sgp.io},
  }