This is a guest post from Greg Toppo, author of the book The Game Believes in You: How Digital Play Can Make Our Kids Smarter. He is USA Today’s national education reporter.

Video games engage us more effectively and more productively than almost any other activity we have come up with. This is why video games make us genuinely happy.

The first question that always comes up when we talk about this research is What kind of game?

Players get different benefits from different games. World of Warcraft, a massively multiplayer online role-playing game, or MMORPG (it’s often shortened simply to MMO), offers a level of immersion, an epic sense of accomplishment, and a sense of fellowship with other players that a simple iPhone game like Candy Crush can’t match.

But even simple games are thoughtfully and cleverly designed, sucking players into what sociologist Natasha Dow Schüll calls the “machine zone,” a mental state where nothing else matters but a player’s ability to keep playing. Schüll has spent years studying Las Vegas slot machine players. She found that the most obsessive players don’t actually play to win. They’re “time-on-device” players who “play to win to play.” Sound like any Candy Crush devotees you know?

Actually, video game advocates would take exception to the slot machine comparison, and with good reason. Slots don’t require much in the way of ability, and they certainly don’t reward failure in the same open-hearted way that a video game does.

In fact, video games stand apart, not just from slot machines but from nearly every endeavor in our lives, in this way: we’re disappointed if mastering one is too easy. Imagine being disappointed to find that operating a snowmobile, filing your taxes, or mastering calculus was easier than you’d thought.

As for the difference between World of Warcraft and Candy Crush, players get the problem-solving benefits with either one, as well as a generous dose of something game theorists call “flow” or “optimal experience.” First identified in the 1980s by Hungarian psychologist Mihaly Csikszentmihalyi (pronounced “chick-CENT-mee-hi”), it’s a mental state in which a person’s abilities match the task at hand so perfectly that the work becomes invisible.

Situated midway between boredom and anxiety (skills without challenge equal boredom, while challenge without skills equals anxiety), flow emerged from Csikszentmihalyi’s work studying, among others, painters who became so consumed with their work that they ignored the need for food, drink, or sleep. “The best moments usually occur when a person’s body or mind is stretched to its limits in a voluntary effort to accomplish something difficult and worthwhile,” he wrote. “Optimal experience is thus something that we make happen.” It’s also, he found, a key element to happiness.

Although most Americans enjoy a fair measure of free time and ample access to leisure activities, Csikszentmihalyi found, they don’t often experience flow. Watching television, which we do for about thirty-four hours a week, rarely leads to flow. Csikszentmihalyi found that people actually achieve the flow state — “deep concentration, high and balanced challenges and skills, a sense of control and satisfaction” — about four times as often on the job as when they are watching television.

Video games, from the simplest to the most complex are, in a way, perfect flow machines.