Here at SWA we monitor all the Macbooks in the school using Apple Remote Desktop. It is truly a powerful tool that enables all teachers to see the student's screens whenever they need to. Our IT Tech Dept monitors every screen in the school. We use an Internet filter but Remote Desktop enables us to interact with students through chat, control the screen, view a whole class at once and lock the screen.
As a teacher I like to use it to guide the students in their work. I send messages about what they are doing to help guide the students more individually. You might argue that walking around the class has the same effect. For me Remote Desktop allows me to send my students off to work on a project in a quiet place away from the classroom. I don't have to worry that they will be off task as I can see their screen and know what they are up to.
On the technical side our on site technicians can help students with troubleshooting remotely. Just yesterday in Grade 3, one of the students was about to use iMovie to edit a documentary, only to discover that his laptop (from the laptop cart) had iMovie '08 instead of '09. I used iChat to contact our Tech Dept and they were able to install iMovie '09 remotely.
The photo shows the student waiting for the update with his screen locked via Remote Desktop so that he cannot press the wrong key during the installation. The problem was solved within 10 minutes.