Very briefly, when I was with the Sentencing Commission, we commissioned some research on the theme of the prison being the university of crime. We asked our researchers to give us quotes in official documents from the birth of Canada up until now.
You can look at the report. There is one quote to this effect about every three years, and it goes all the way back to the invention of prison. So I would say the most recurrent leitmotif in all the literature of incarceration is that yes, it hardens criminals and teaches them new tricks.
The silent system, which was first envisaged by the Americans, was for prisoners not to talk to each other, so that they would not teach each other new tricks. This is the commonplace in the literature on incarceration.