I would still suggest that you get some experience working for a regular school district first, since that is generally a basic requirement for PhD admission and then for a faculty job in academia that would allow you to pursue the research you love. Especially if you are interested in juveniles who have interactions with the juvie system, you will find that you'll have plenty of opportunity within a school district setting--at least in most middle and high schools. A couple of the schools that I taught at had self-contained settings for children with severe behavioral issues who could not be accommodated in a regular classroom. The overlap of that group with kids who had been in the system at least briefly was near 100%. Also, there was considerable competition among our SpEd folks to NOT teach that group, so you could probably get all the experience you want, if you express interest in this kind of a job when interviewing with a district.
And many/most education jobs in the juvie system are run by the local school district, so the route to hiring leads through the school district anyway.
You are truly on the side of the angels, Flamglam! This kind of work is desperately needed if we're not going to keep losing generations of our youth, and there are very few people who are interested in it and committed to it. MrP and I volunteered in the prison system in our old location for 15+ years, and I used to go into juvie, too. I also had a lot of students who were back and forth between my classroom and our local youth facility--which was, conveniently, right down the road.
Ms P., thank you for your encouragement and support. It is most appreciated and very helpful, and I'm quite excited about furthering advocacy, understanding and scholarship for this particular population of student - the true "throwaway kids" in our society, particularly if African-American and male.
Incidentally, one of my teaching assistant positions was for an alternative school serving residents of an all-male juvenile sex offender facility. That was my first exposure to teaching AND to this population, and I loved both.