Saving money. Most superficial reason. Proprietary software companies started to give gratis or nearly gratis copies of their software to the educational institutions.
Educational system should not make society depending on the proprietary software. Schools shall reject gratis copies of proprietary software for the same reasons they reject
free samples of addictive drugs for the students.
Education of best programmers. If software is proprietary student can't study its source code and education is not possible. Studying how to program is not studying how to write small programs. Students shall start from writing small parts in large programs. Free software gives this opportunity.
Ethical education. Education in citizenship. Schools teach above all to the spirit of good will, habit to help the neighbor. Schools shall give examples of ethical behavior. Which is
not possible with proprietary software.
Students and teachers - pressure your school to move to the free software:
Make the people aware that usage of non-free software is wrong.
If you are student and you have a class where proprietary software is used stand up in the very first lecture and ask to help you to find a way to make the work of this class with only free software. Explain that you are ready to work harder and understand possible inconveniences.
Your readiness to inconveniences shows that you are serious about freedom and influences other people around you.
This campaign shall be big. Don't expect that the battle will be won without you.
Upgrade from Windows! It's not possible to live in freedom with Windows. Any version of Windows. Don't downgrade to Windows Vista at least.
Learn how to make easy changes:
Anybody can exercise Freedoms 0 and 2 (see lecture 1.2) - the freedom to run the program as you wish, for any purpose and
the freedom to redistribute copies so you can help your neighbor.
Freedoms 1 and 3 (see lecture 1.2: the freedom to study how the program works, and change it so it does your computing as you wish
and the freedom to distribute copies of your modified versions to others) require programming skills.
It's useful to learn how to make easy changes in the software. You don't need to become software engineer in order to be able to do them. Analogy: it's useful to know
how to make small maintenance of your car even if you are not a professional mechanic.