The student computers in the library classroom were not equipped with speakers for obvious reasons. I have made most of my games without sound effects, which does help when trying to limit the file size of the games. However, sound is a critical part of the gaming experience. I have been struggling to give visual clues to students when an answer is right or wrong, but it interferes with their activities, which is a big no-no in game development. They should not have to wait for the "Correct!" image to fade before they can click on the next item. A simple bling or gong sound would allow them to know immediately if they got something right or wrong without interrupting their progress.
We are in the process of ordering some relatively cheap speakers for those computers specifically for my games. I hope they will arrive soon, though it's too late to use them in classes this year. This morning, I started putting sound into my plagiarism game. I am getting most of my sound effects from The Freesound Project. I don't think I'm going to go so far as to put music into my games, at least not yet. However, I found a great juicy-sounding splat noise when an answer is correct since the player is supposedly killing goblins, and a nice water noise to play when the player clicks on the courtyard's fountain.
Everything I have read has stressed the importance of the gaming experience to make the learning part less noticeable to students, and sound is definitely important to the experience.