Alice Marwick and I co-authored this piece for The Guardian.

The Press Complaints Commission in the UK has now ruled that there is no “reasonable expectation” of privacy on Twitter. With this decision and the fact that teenagers are flocking to Twitter in a big way, frustrated adults are asking the same questions of teen Twitter feeds as they did of MySpace and Facebook: don’t young people know this stuff is public? Why do they put personal things online? Why don’t teens care about privacy?

First, let’s get something straight: not all teens use Twitter, and those who do don’t all use it in the same way. The sense of what’s appropriate on Twitter varies wildly by social group and locale – is it OK to break up with someone on Twitter? To tweet a hundred times a day? Similarly, young people use Twitter in different ways. Some primarily follow celebrities, enjoying the glimpses into their lives, sending @replies to their favourites in the hope of a response and chatting with other fans. Others like getting coupons and freebies from Twitter-savvy brands. Still other teens use Twitter to play hashtag games, like #lessambitiousmovies (think “The Devil Wears Payless” and “The Above Average Four”), where their bon mots can be retweeted or commented on by thousands they may not know. There are also countless teens who use Twitter primarily to engage with people they know from school, summer camp or after-school activities. Who teens imagine reading their tweets very much shapes their style of participation.

Twitter gives its users two settings: make tweets readable to all, or only to a selected group. A surprising number of teens choose the latter, culling a carefully chosen collection of real-life friends and family members. Even for teens who keep their tweets public – like the overwhelming majority of adult users – Twitter seems smaller and more intimate than Facebook. In an age where virtually every young person has a Facebook account, many teens are “friends” with hundreds of classmates, as there’s heavy social pressure to accept friend requests from people they know. Twitter’s more casual approach to “following” means teens can choose to follow only their friends without too much recrimination. In North Carolina, 17-year-old Manu summarises this sentiment: “I guess Facebook is like yelling it out to a crowd, and then Twitter is just like talking in a room.”

To teens, Twitter and Facebook have different purposes. Matthew, another 17-year-old from North Carolina, told us: “On Facebook, if someone writes their emotions every five minutes, it’s just obnoxious.” Since it’s normal to have 600 friends, if one of them posts constant status updates, it potentially drowns out more important or interesting messages. Matthew and his friends call this “blowing up your news feed” and it’s looked down upon. But on Twitter, it’s perfectly OK to talk about the meal you just ate, or the moment-to-moment sadness you feel, because the site encourages such minutia – and you can always unfollow someone if they tweet too much.

It’s also important to remember that just because a tweet can theoretically be accessed doesn’t mean it will be, nor does it mean the underlying sentiment will be understandable to an outside audience. Plenty of teens – and adults – use aliases and nicknames for their Twitter account, since unlike Facebook, Twitter doesn’t require a real name. Twitter also allows more playfulness; among the most popular Twitter accounts are a cat and several fictional characters.

But even when teens aren’t hiding behind monikers, what they post may not make sense to an outsider. Access to content is not the same as access to interpretation. Teens regularly post in-jokes and use song lyrics or cryptic references to speak to a narrower audience than might be accessing their tweets. Some tweets are clearly difficult to decode, making the reader aware that a message is being hidden; others can be understood as “social steganography” where the message is hidden in “plain sight”. While their classmates, parents or potential employers may be able to see these tweets, they don’t necessarily understand them. Although there’s nothing fundamentally new about these practices, their application to Twitter makes it clear that teens are aware of speaking in public and using strategies to manage it.

What all this means is that “public or private” is more complicated than it seems. Twitter and its ilk aren’t going away, and the answer to responsible use isn’t to shut teens out of public life. Many teens are indeed more visible today than ever before, but, through experience, they’re also developing skills to manage privacy in public. What matters is not whether or not teens are speaking in public, but how we support them as they try to learn how to responsibly navigate the networked public spaces that are central to contemporary life.

More comments can be found on the thread at The Guardian.