Ubuntu is 100% Linux (based on Unix )  which is Open Source and is the product by thousands of world class programmers contributing their code    sharing their expertise with the Linux project voluntarily    as the part of community .
Ubuntu by far is most usable user friendly Linux variant ever  . Ubuntu is based on Debian    which powers most of the Corporate Servers . It contains over 20  000 Software Packages available for being installed .
Unix / Windows being proprietary hampers growth of programmers as they can never have complete control over the machine / can never know how things work deep inside the OS. Linux on other hand allows users to customize it the way they want being open source it allows users to look into the code  modify the code and play with it .
Having made source code of an operating system available to 6th graders is like allowing them to do open heart surgery. The more they will experiment with it    the better understanding they will have about  “How & Whys”  of functioning of either of them  .
Linux is relevant everywhere    be it Mobile devices ( Android is powered by Linux Kernel )    Computers in Homes    Industries   Government Offices .
Linux is powering thousands of Servers of Google    Facebook    Twitter and majority of  Fortune 500 Companies . Companies like Oracle    Google    Facebook also openly supports  and contributes to Linux Project .
Linux supports all major programming  languages like Java    C    C++    PHP    etc .
Windows usage is ever declining ( Domestic & Industrial ) because of its long list of Demerits : Security Flaws    Bad performance over time    less control over machine    to name a few .
Linux is supported by million users strong community    Corporations like Canonical which is behind Ubuntu    Edubuntu    Kbuntu    RedHat which is behind Fedora    Red Hat Linux which powers servers of majority Fortune 500 companies .
To be part of Open Source Community    Linux happens to be prerequisite as it’s first step in the ladder. Linux being World’s largest Open Source project powering millions of machines ( Desktops / Servers ) worldwide.
Every year Google conducts its programming event called “ Google Code-Jam” for international school students in which 100% participating organizations are Open Source Based. Students work on project with any organization they like . Google rewards them after successful completion of project .
All Supercomputers in entire world are using Linux as their primary OS [6]
Beside that majority of Departments of US government switched to Linux    Fortune  500 companies like Oracle are using Linux for its security    stability & performance .
Linux / *nix is included in Engineering / Any Computer Science Courses in every University around the Globe .
We at Schools are building futuristic children    who can explore the world and gets their hand on latest technologies available in IT domain . The sooner the children will start using linux    the better  they will get overtime .
As Schools is going Open Source   Students will  have access to knowledge about technologies working behind Servers / Mobile Phones / Any Computing Device or which they are using .

References :
[1] http://en.wikipedia.org/wiki/Open_source
[2] http://en.wikipedia.org/wiki/List_of_Linux_adopters
[3] http://www.westhost.com/blog/2012/12/24/fortune-500-companies-drool-over...
[4] http://www.linuxfoundation.org/publications/linux-foundation/linux-adopt...
[5] http://www.slideshare.net/linuxmalaysia/linux-open-source-usage-in-the-f...
[6] http://en.wikipedia.org/wiki/Supercomputer_operating_systems