To be honest I haven’t really done the proper research on this and this is mostly speculation, but if it becomes important to my project (which is a possibility) I guess I’ll have to, somewhere. Basically, there are three main ways in which games that are not directly educational can teach us. These are by mechanics, narrative/storyline, and by extension.
Learning by Mechanics: This is where the actual controls and interface you use are what teaches you; the framework of the game over anything else. Card games like Yu-Gi-Oh and Pokemon with numerical based systems can teach quite advanced mathematics to young children – though whether they can access that information outside of the game world is possibly another story. Most video games help improve basic hand-eye coordination, but first person shooters such as Call of Duty or Halo are particularly good for this (in my opinion?) as they involve having to walk, change camera views and shoot simultaneously while also having to keep track of the overall map, your health and weapons and your current position in the game. Research has shown that this ability to take in a lot of things at once does transfer to real life. My third example is Portal, whose basic mechanics apply strictly to the rules of physics. The player grows to understand these rules as they progress through the game, and then has to apply them to complete levels.
Learning by Story/Narrative: Sometimes a game will have realistic historical context, or contain real people and figureheads. Children are more likely to take note of these facts, presented to them in a form they are interested in (i.e. the game) than they are in the classroom where they feel they are being forced to learn. Humans are built to learn. We enjoy it. The issue with schools is the manner in which they go about trying to facilitate learning. Hugely popular games that have taught millions of kids historical facts like this are the Age of Empires series and, more recently, the Assassin’s Creed series.
Learning by Extension: This way of learning takes the education out of the game itself and puts all of the responsibility of learning onto the player themselves. Basically, learning by extension is including objects, facts, names – anything, that means something “in real life”. Final Fantasy is a great perpetuator of this technique, stealing names for items, weapons, ships and characters from all over the place. For example, all of the summons in FF games are taken from various mythologies and religions around the world; Bahamut (Arabic), Shiva (Hindu), Odin (Norse) for example. Now that might not mean much if it wasn’t for fandoms. Maybe 1 or 2% of people will get so into a game or character and then look it up online, but when they do they might find a “did you mean” which, if they are interested, might lead them on a whole new journey. For example someone looking up Shiva might be amazed at the ideas behind the original Hindu deity and decide to learn more about Hindu gods, or even Hindu culture in general. This is how learning by extension is created; a self-led path of discovery.