I can't answer that.
You may have noticed that I tend to have opinions about things, and I'm generally not shy about sharing them, especially when my opinions are well-researched and science-based. If you ask me about children zero to three and screens, I'll tell you my opinion:
TURN IT OFF.
I don't care if it's an educational game on the iPad, or Sesame Street, or Angry Birds. It's not good for your child's brain. I feel so strongly about this that I made Boo turn off the iPad when my 1-year-old niece was attracted to the screen.
There are exceptions, of course. Boo watched a few hours of TV in her 0-3 years when we were on an airplane, when she was sick and screaming while I waited for the Tylenol to kick in, and (of course) the Olympics. And I was able to take this principled stand because my husband came home at 3:45 every day and took over baby care. And I have only one child. So if it's 4:30 and you're going to kill your three kids if you don't turn on the TV, then by all means--turn on the TV. It's easy for me to say I didn't have to--I didn't have to.
As Boo has gotten older, we watch more TV together. She loves movies, so we watch a lot of those. We also like watching some educational stuff together--nature shows, shows about Ancient Egypt, and science shows. Sometimes when I can see that Boo is too tired to handle herself well, we even watch these things on school nights. And she loves Tabletop.
And this is why I can't answer the question about screens in classrooms. Because every situation is different, and while it's clear that very young children learn by doing things and don't learn by watching things (screen-type things. They do learn by watching actual things, like a person building with blocks) this becomes less true as kids get older. However, it is pretty much always true that people learn better by doing than by watching and so there should always be a healthy dose of doing in the classroom.
On the other hand, some things have to be demonstrated ahead of time, and video or computer-based animated text can be good at that. Some things you can't bring into the classroom, like Tibet, and photos or video are great for showing those things. Some things need to be documented, and SmartBoards allow the teacher to keep a record of what was written on the board, which is really useful sometimes. And some things are just too dangerous, too expensive, or too restricted for kids to do themselves. (Just try getting a permit to take a field trip to a construction site.) Video is great for those things.
SmartBoards are also a great way to teach kids how to use computers, which is something we want kids to learn before they graduate high school.
Can you teach these things without SmartBoards? Of course. Can a SmartBoard be a total waste of money? Absolutely. But in the hands of a masterful teacher who knows how to use a SmartBoard well and integrates that tool into a lesson, it's a great thing (for older kids.)
I would NOT want to see a SmartBoard below first grade. Younger than that, kids should be doing things: building, practicing reading and writing skills, counting, making things, and playing with other children to develop social skills. I would want to see it used sparingly in the younger grades for the same reason. Up to about age 9 kids have not fully developed abstract thinking and still need concrete examples (doing things) in order to learn. And they need lots of time to play.
But after about age 9, most children have developed the ability to think abstractly, and they can then learn from screens quite well, although as I said, learning should always involve a healthy dose of doing stuff.
So how do I feel about screens in classrooms? If they're used well, they're great. If they're not, then they are a waste of money. What you need in a classroom is a great teacher, and then you should buy that teacher the tools she needs to teach the way she teaches best. It's really not about the screens.
But at home, less is more. I should say that I love TV. I considered getting a Master's in it. Seriously. So it would have been really easy for me to turn on the TV when Boo was little and watch all the kid shows. I would have enjoyed it. But whenever I was tempted, I thought, "What will we do if I don't turn on the TV?" Again, if the answer is, "I'll beat her to death," then please--turn on the TV. But if the answer is frisbee (as it was for me on Monday, when I played this game with myself for the eleventh-billionth time) or reading a book, or having a chat, then don't turn it on. Do the other thing instead.