Assuming you have a Chromebook or school PC with internet access, here is the fastest way to play Minecraft free unblocked in less than 2 minutes.
For those looking to play Minecraft entirely for free without downloading files or circumventing heavy security protocols, Minecraft Classic is the best legal solution.
Released by Mojang to celebrate the game's 10th anniversary, Minecraft Classic is a browser-based version of the game. It recreates the original 2009 creative mode, allowing players to place and break blocks in a 2D/3D world.
If your school’s firewall is extremely strict and blocks all unknown sites (like GitHub), you can use the official Minecraft Demo.
If you can run the launcher, the Demo gives you 100 minutes (or 5 in-game days) of survival mode. Once the time runs out, you cannot regenerate the world without resetting your Minecraft directory.