High School students learn programming with Linux

rarkian writes: I am the teacher in this story . I teach Python and C++ to high school students: grades 9-12. I use CentOS 6 with DRBL to run my computer lab. Some of my students have become Linux experts. Next year I'm planning on allowing students to create and run their own VM's in a segregated LAN. Any advice on which virtualization technology to use and security concerns with allowing students to be root in a vm?