Well some video games I wouldn't classify as "Art", just the same as some Movies I wouldn't consider "Art" and some music I wouldn't call "Art". It depends on the quality of the game. For instance, I wouldn't call Call of Duty: Black Ops, Art even though it happens to be a game that I consider to be loads of multiplayer fun.
At this point you'd have to define what YOU consider art is. If you want to step back, I consider all three mediums Artistic Mediums. But just like everything else most of it is abused for different reasons. Action movies that appeal to the masses (EXACTLY like Action Games that appeal to the masses) are typically never there to do anything besides make money. There are exceptions to every rule.
Your teachers attitude is unsurprising, as previously stated, because she's had little experience with the medium. If she were to play Shadow of the Colossus, she'd probably have a completely different opinion.
That being said, unlike in Writing and Movies, I find that there are far fewer examples of Video Games that you can claim wield a high level of Artistic Integrity, especially as games continue each generation. There seems to be an almost universal level of Action, Zombies, and other atypical genres going around nowadays, in both gaming and film, that are made specifically to attract John and Jane Doe into THINKING that they're experiencing something out of the ordinary.
Example: Mass Effect, great game, brilliant narrative, Bioware's focus on dialogue driven exposition shines through better than any other, but is the game artistic? In my mind, even being a fan of the series, I can't consider it to be anything other than what you can expect when the technology becomes available. Both games' stories have been subpar, the levelling systems have been a reflection of what is considered popular, the first being a near Diablo Clone, to the second being Gears of War lolworthy, and while I've been drawn into the experience I can't say that I came out of it thinking that the entire gaming industry would do itself well to take a page out of Bioware's book (except maybe the dialogue writing, not necessarily the selection).
Example 2: As opposed to Mass Effect, there is still a high action game that deserves mention if you want to talk about Artistic gamine in the recent generation and that of couse is Bioshock. Between the story you have to explore to find and the atmospheric world that tells a story in itself, Bioshock is beautiful and terrifying to look at, a brilliantly original idea (to a point) and even offers one of the most mind bendingly fourth wall breaking twists of any game ever, it provides an interesting backdrop for what is actually a very mediocre and too often seen game that prevails only in proving why more games with Bioshocks system aren't being made.
Gaming CAN be artistic, the same way that Music and Film CAN be. Your teacher just hasn't seen the right stuff yet. You think I realized how wonderful film could be before I saw The Godfather? Shawshank Redemption? Did I realize how moving music could be before hearing Metallica? Queens of the Stone Age? Pink Floyd? Can someone really realize how great gaming is without having played Final Fantasy 7? Shadow of the Colossus? Bioshock? Majora's Mask?
The answer, is no.
