The Chester Community Charter School in Chester, Pennsylvania, with roughly 2500 students, is the largest pilots of XOs in a charter school, and one of the largest single-school pilots in the US. They began in 2008 with 1400 students in 6th through 8th grades, and have since added over 600 more students in 3rd through 5th grades.
They planned their infrastructure and teacher preparation carefully — adding a high-bandwidth network connections within their school to handle the dramatic increase in Internet usage they expected, and running regular workshops with the head teachers from their 3 initial grades to develop new materials to make use of laptops in and out of the class. And they have engaged city and state policymakers and other potential supporters in their area from the beginning.
I helped them with the initial deployment and a school-wide demonstration we gave to the students — and I still remember the joy with which they glommed onto the new machines; the teachers full of ideas after some brainstorming, and the students pepped by our demonstration of a competitive two-player Maze session. They recently asked to test out the 1.5 and future tablet models, and seem to be growing their student body steadily at over 10% a year. I hope to visit with their teachers again soon to see how this has changed their views of teaching.