The phrase "model prisoner" refers to someone who behaves very well while they are in prison. They follow the rules, respect others, and show good behavior. Full definition
«Kent is neither a model prisoner nor a player tortured by doubt,» says TV analyst Chris Marlowe, captain of the 1984 U.S. Olympic volleyball team. (si.com)
She is not eligible for parole until 2056 despite having been portrayed as a model prisoner by Dennison, the prison's former warden and several others. (theexaminernews.com)
Judy Clark, a lesbian who was convicted for her role in the 1981 Westchester County Brinks robbery, a headline - grabbing crime staged by the radical Weather Underground that led to the murder of two police officers, has been a model prisoner, according to widespread accounts. (gaycitynews.nyc)