From the perspective of most schools, the big advantage of open source software is that no-one is demanding payment for licence fees, either outright or as annual subscription. That's not to say that it's without any costs, but training, support, maintenance and, for web-based applications, hosting, are costs which apply to all software, whether open source or proprietary. Back in 2005, a small scale study by Becta identified significant savings in the total cost of ownership for open source schools, not only for licences but also for hardware, training and support.