I’ve ordered this list according to my own educational values:
Open-tools promote equality. Open-tools allow students to use the same tools as the teachers. They allow the lower income students to use the same tools as the ones with more resources. Open hardware can be given away free to needy students.
Open-tools decentralize the creative process. A project can be started in the classroom, continued in the library, finished at home and presented in the classroom, all using the same tools.
Open-tools and content promote ethics. If a student needs a software tool at home, s/he can download and install it without stealing. Open-content can be honestly used and shared.
Open-content encourages a culture of creating and giving. People who share their content are good role models for contributing citizens.
Open-content promotes information literacy. It encourages students to consider who created something and why.
Open-tools sell less stuff to our students.
Open-hardware is more green. Lighter weight tools, like Linux, give hardware one more useful incarnation before heading to the landfill.
Open-tools help gifted students. TAG students or computer clubs can get “under the hood” to improve a tool and contribute to the open-source community.
Open-tools make sharing documents easier. If everyone is using the same set of tools, sharing files is much easier.
Open-tools make upgrading easier. No need to wait for funds or hassle with having old versions on various machines.
… but to be fair:
Open-tools are not always cheaper. They are free but they can take up more of your valuable time, adding to the cost.
Open-tools are not always better. Sometimes they are decidedly inferior! This has greatly improved in the last decade but open-tools generally lag behind their commercial counterparts. However, if you stick to the most popular software, you can get the job done.
Open-tools are not always easier. Again, this has improved. I, personally, find LibreOffice easier than Microsoft Office because LibreOffice has fewer features cluttering things up — features which I don’t use anyway. I also find upgrading Ubuntu easier than finding, buying and upgrading Windows.