It seems like trusting teens just the right amount is an impossibly fine line to walk. If you trust them too much and they take advantage, that could damage the relationship or they could get into serious trouble. If you trust them too little, they don’t have as much confidence, and they may grow to resent you for it.

When it comes to teens, trust is a two-way street that has changed over the last decade or so with the arrival of apps and devices that help parents track their teen's social media accounts, text messages and even driving habits. But while it may feel like spying to read another person's email or track their whereabouts, it's not spying when your teen knows she's being monitored, says Dr. Michele Borba, an educational psychologist and best-selling author of "UnSelfie: Why Empathetic Kids Succeed in Our All-About-Me World."

"Safety is always the top priority when it comes to parenting," says Borba. Parents absolutely should be monitoring their teen's activities — both online and off. And as she explains, here's why:

1. Being online poses certain dangers. Inappropriate content, cyberbullying, online predators — the internet is not a completely safe place. One in five kids receives sexual solicitations online, and more than 30 percent of kids online have experienced some kind of online harassment, Borba says.

Your child's image and reputation could be in danger, too. "Inappropriate posts or photos could jeopardize a college acceptance or job. And 39 percent of teens admit posting something they later regretted," says Borba.

2. Teens lack impulse control. Teens' brains are still forming, and the circuitry that activates good judgement may not be in place, Borba says. That may explain why 54 percent of teens admit to risky online behavior, 40 percent admit they gave out personal information, and 64 percent say they do things online that they wouldn’t want their parents to know about.

3. Hands-on parenting lessens risky behavior. If there's one thing kids need from us, it's for us to be present. Hands-on parenting means monitoring behavior, knowing your kids’ friends, setting clear rules and not being afraid to say no. "Study after study proves that the best protective action you can take as a parent is to keep the lines of communication open with your teens," says Borba. "Studies also show that parents who are most successful at raising kids who have strong identity, self-control, self-esteem and character are parents who provide less permissive environments."

How to monitor your teen

Teen on his phone You can monitor their activities while respecting still their privacy — which they're entitled to have. (Photo: Iakov Filimonov/Shutterstock)

"Teens are less likely to do risky behavior online and offline if they know they’re being monitored, even intermittently," Borba says. You can monitor their activities while respecting still their privacy — which they are entitled to have, she says. "Let your teen know that you will honor his or her privacy. No reading her diary or going through her drawers. But those rules are immediately broken if you have any founded concern that your teen’s safety is in jeopardy."

1. Involve them from the start. "Tell them you will monitor, but don't tell them when or how often you’re monitoring. Many parents every once in a while will say, 'Turn in your cellphone, and let's make sure you’re abiding by the rules of the house,'" says Borba. The child has to build your trust, she adds, and when he can demonstrate responsibility, then you gradually let him have more and more responsibilities and freedom.

Say your tween wants to join Snapchat or Instagram, for example. Borba says if your child is on the platform, you need to be there, too. Tell your child that you will not post on their account, but you will check it periodically so they need to share their login information and passwords with you. You can even have them help you set up your profile or account so they're engaged in the process. Borba says she's heard from several teens who say they're glad parents are on social media, because a lot of the kids behave better when they know an adult is checking.

2. Learn their language. Parents need to know teen shorthand and acronyms so they can understand what they're reading. For example, MOS means mom over shoulder, KPC means keeping parents clueless, LMIRL means let's meet in real life and GAP means got a pic. Google "texting abbreviations" or "online language" and you'll find cheat sheets, Borba says.

3. Set rules for sharing. Teach kids that there are no "take-backs" when it comes to the internet, and they should think about what they post as being live for everyone to see forever — including Grandma, Borba says. Teens should not share personal information, such as full name, birthday, address, passwords, school name or social security number, as this makes them easier to locate. If you find they break these basic safety rules when you're monitoring, make sure there's a consequence.

4. Take advantage of tools and apps. Parental controls, internet service providers, computer software and various apps can monitor texts and emails, block visits to inappropriate sites (hate sites, pornographic sites) and email you reports of their online activity, says Borba, though she acknowledges that tech-savvy teens can figure out how to get around such things. She suggests being honest and telling your child that you've installed software. "Just don’t divulge what kind," she says.

5. Set curfews, and definitely wait up. "Peer pressure is huge. Teens need safety nets. There is no better excuse than for a kid to be able to use than, 'Mom will ground me for life if I don’t get home.' Do tell your teen that he or she has your full permission to always use you as an excuse," says Borba. Plus, she adds, teens need sleep, and nothing good happens after midnight.

Part of monitoring happens when a teen comes home after a night out. "Check in with your child, give them a hug, smell them, check ‘em out," she says. You can be subtle (and sleepy), but, again, be present. If your teen knows he'll face a parent when he walks in the door, he'll be less likely to engage in risky behavior while he's out.

6. Be their safety net. You may have seen a recent viral story about a dad who gave his teen son a way to safely get out of social situations when he's uncomfortable. Sometimes teens feel they can't call or text for help because other kids will hear or see. So this duo set up an escape system where if the teen texted the father an "X," the father would drop everything to come pick him up, wherever he was, no questions asked.

Borba says it's an excellent system, and it doesn't matter whether it's an X or an ABC or whatever. Here's the catch, she says: You have to honor the "no questions asked" part. She has heard from kids who've tried this emergency escape plan only to get the third-degree from a parent later on, and they never used it again.

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.