Some of the games and classes required my students to write things down and fill things out. They certainly couldn't do that with regular Muggle pens, so I made a bunch of quills out of feathers and plain green Bic pens.
At first, I simply taped the pens to the backs of the feathers. But I later received a tip from a fellow witch that involved removing the outer tube of the pen and inserting the center well into the shaft of the feather. The look is much more streamlined and convincing!