When I was a kid, my parents had strict television rules: no more than an hour a day, and the content must be educational. This meant a lot of PBS. I did briefly convince my mother that the secret-agent show “MacGyver” was about science, but that boondoggle ended when she watched an episode with me. These restrictions seemed severe at the time, but my parents were just following the orders of the American Academy of Pediatrics (AAP): Children and teens should have no more than one to two hours of screen time per day, with children under 2 having no screen time at all. Those orders remain the same today.

Relative to my childhood, limits on screen time have become increasingly restrictive and confusing. The iPad (and Kindle, and various other tablets) has opened up a world of “educational” screen time. If my 4-year-old is doing a workbook on the iPad, does that mean she learns less than if we used a physical workbook? The AAP advocates for newspapers and physical books over iPads, computers and other screen options.

The AAP statement on media seems opposed to screens per se (quote: “young children learn best when they interact with people, not screens”) without really differentiating among various uses and types of screens. But, not surprisingly, when you look at the research, the screen matters less than what you do with it.

Of all the possibilities for screen time, television watching clearly gets the most negative attention. It’s not hard to see why. Unlike educational games on a tablet, which at least can be argued to have some interactive value, television and movie watching are largely passive. Those who oppose TV for children worry about many downsides, but chief among them are declines in test scores (or other cognitive ability) and increases in obesity.

Let’s consider a few examples. This paper relates television viewing among preschoolers to measures of “executive function” — basically, whether a kid can focus and accomplish a goal — and finds that more television exposure is associated with lower executive function. This one looks at a large sample of children and associates television viewing at younger than 3 years with lower test scores at ages 6 and 7. And this one relates television watching to obesity among children.

These are a small number of the many, many studies that show associations between time spent watching television and health and development outcomes. But all these studies have an obvious problem: the amount of TV children watch is not randomly assigned. In the general population, kids who watch a lot of TV — especially at young ages — tend to be poorer, are more likely to be members of minority groups and are more likely to have parents with less education. All these factors independently correlate with outcomes such as executive function, test scores and obesity, making it difficult to draw strong conclusions about the effects of television from this research.

There are a few studies with better designs, and these have mixed results. There does seem to be some evidence to suggest that lowering media consumption, including television, can help combat obesity in children (see here and here for examples).

The impacts of TV on IQ and test scores have not been subjected to large randomized trial evaluation. Perhaps the best causal evidence on this question comes from a 2008 paper by two media economists. The researchers take advantage of the fact that television was introduced to different areas of the United States at different times. This variation meant that, when television was first introduced in the 1940s and 1950s, some kids had access to TV when they were children and some did not. The researchers could then see how having TV access as a young child — what the AAP is most worried about — related to test scores when kids were in school at slightly older ages.

The researchers find no evidence that more exposure to television at an early age negatively affected later test scores. The contemporary applicability of this research is subject to various concerns — television in the 1940s and ’50s differs from the TV of today, for example — but it does suggest that such concerns about test scores may be overblown.

A second set of concerns with television — and these extend to all other screen time — is that there is something inherently bad about exposure to a screen per se. There really isn’t anything in the research to make us think this is a concern. Even the AAP, the ultimate screen time naysayer, focuses in its warnings on attention and learning difficulties, obesity and risky behaviors resulting from screen time.

Some parents worry about eye strain from looking at screens, but, again, there is simply no evidence for this. Looking for “iPad and vision” (or “tablet and vision”) in the medical literature results primarily in papers about using iPads to help people with poor vision read better. If you’d rather read your kid a book on the Kindle than on paper, there should be nothing to give you pause.

Based on my read of the evidence, I’d say there’s absolutely no reason to think there’s anything worse about using a screen to do activities you would otherwise do on paper. When it comes to passive screen time — TV and movies — it seems that, on average, watching more TV has limited (if any) impacts on test scores, but maybe has some small impacts on obesity among children. However, the key phrase here is “on average,” and fleshing this out makes clear why the effect of television is such a difficult issue to study.

To judge what impact TV has on children, we have to think about tradeoffs — what would kids be doing with their time if they weren’t watching television? There are 24 hours in a day. If your kid watches one less hour of TV, she does one hour more of something else. The AAP guidelines imply that this alternative activity is something more enriching: reading books with dad, running on the track, discussing current events with grandma, etc.

But a lot of kids and families may not use an additional hour in these ways. An hour of TV may be replaced by an hour of sitting around doing nothing, whining about being bored. Or, worse, being yelled at by an overtired parent who is trying to get dinner ready on a tight time frame. If letting your kids watch an hour of TV means you are better able to have a relaxed conversation at the dinner table, this could mean TV isn’t that bad for cognitive development.

With this insight, it’s easy to see why less television is likely to decrease obesity. The process of weight gain and loss is pretty simple: if you burn more calories than you take in, you’ll lose weight. Watching television is mostly done sitting. And most other activities involve at least some moving around. So pretty much no matter what else they do, watching less TV is likely to be associated with kids burning more calories and losing weight.

Similarly, it is easy to see why TV might not affect test scores. If the alternative use of an hour for most families is not in highly enriching parent engagement, television may be just fine.