What’s the simplest cheap setup for a classroom of offline Linux workstations?

For donated equipment, check local computer recyclers, businesses replacing office PCs, and school or municipal surplus programs. A wired network with a basic switch is more reliable than Wi-Fi if you do use thin clients. Before choosing the design, decide whether students need shared files, printing, or internet access—if they only need LibreOffice, independent offline computers will probably be the cheapest and least complicated solution.

Debian Edu is worth investigating instead of assembling all the pieces yourself. It provides a school-oriented Debian setup with installation media, centralized services, user management, and tools for managing classroom computers. It can support filtering and other administrative controls, but it will take some learning and setup time. For a very small lab, separate offline workstations may be simpler than deploying a full server-based environment.

You may not need a network at all if the goal is simply LibreOffice. Install a lightweight Linux distribution on each donated computer, keep the machines off the network, create restricted student accounts, and install only the applications you want them to use. A customized persistent live USB is another possibility: each student could boot from their own USB without modifying the internal drive, although managing and replacing a collection of USB drives can become its own maintenance task.

If you can get compatible hardware, older desktop PCs are often easier to manage than Chromebooks. Install Mint, Debian, or another familiar distribution, disconnect the machines from the network, and use non-administrator accounts for students. You can also use a read-only or immutable system image so that changes disappear after reboot. Local restrictions will stop most casual distractions, though determined students may still find ways around them if they have physical access to the machines.

Those small boxes were probably thin clients. The Linux Terminal Server Project (LTSP) is designed for exactly this kind of setup: one server provides Linux desktops to multiple client machines over a wired network. It can be a good option if you have a reasonably powerful central computer and several lightweight terminals, though the server and network become important single points of failure. Some x86 Chromebooks can also be converted to run Linux, but check hardware compatibility before buying or repurposing them.