My son-in-law is a musician and he and my daughter (who accompanies him) have traditionally gone to one of the prisons in their state to perform music for them around Christmas time. However, starting last year my son-in-law has been going there on his own. My daughter said it was just becoming too difficult because she did not feel comfortable being there anymore. I am not sure what happened to change her mind.
I think it's a great idea. I wish I could do it. Prison is supposed to be for rehabilitation. But many prisons don't offer enough support or opportunity for them to succeed. A writing class could be a huge life changer, even if it's only for one person. Writing can be very therapeutic, and it may help them to get out their frustration and issues in a productive way. I say go for it! You just made me want to get a teaching degree in English so that I can do the same.
A former colleague of mine teaches GED courses at a prison now. Don't know much about it, but I do know he was stunned by the level of ignorance that some of his students exhibited, like not being able to name the current president of the United States.
I'd have thought the first step was to find out if its even something the prison wants or would welcome .. also be aware that there are lots of different categories of prison , and indeed of prisoners within a prison so you need to be clear about who your 'pupils' would be. Also what is their general skill level - you say you want to teach memoirs which is great, but be aware that a lot of prisoners may not have the level of litteracy to do that. The other thing is how much experience do you have of teaching , being able to do something (in this case writing) doesn't necessarily confer the ability to teach it