You likely want your teenagers to come to church with you, but at the same time you don't want their behavior to embarrass you. More importantly, you probably want them get something from the experience. Teenagers -- especially those who don't attend church on a regular basis -- often have difficulty sitting through church services. As a parent, there are some things you can do to help them behave in church and get more benefit from being there.
Frontload your Teens
Teenagers -- younger teens and teens with behavioral issues in particular -- tend to function better when they know what their limits are in a particular situation ahead of time. Talk with your teens before taking them to church. If they aren't accustomed to attending church, explain to them what a church service is like and what you expect of them. For example, you should remind them that they should turn off their cellphones, not talk or laugh amongst themselves or fall asleep during the service. You might also remind them that they should use the restroom before the service so they don't have to get up during the service unless it's absolutely necessary. Try to keep this discussion as positive as possible while still setting necessary limits.
Teens typically learn more by watching their parents. If you want your teens to approach worship services reverently, let them see you approaching the services that way. Behaving properly in church as an adult doesn't guarantee that your teens will always follow your example, but if your behavior doesn't show respect and value for the church service, it's hard to demand appropriate behavior from your kids.
Expect your teens to test their limits occasionally, even at church. That's part of the territory that goes with being a teenager. Unless your teen is displaying extremely distracting behavior, chances are that it isn't bothering anyone else nearly as much as it's bothering you. Most people in church have (or had) kids. They understand that teens occasionally misbehave and are glad to have them in church anyway. Correct poor behavior when you need to, but do so with grace.
Sit as a Family
Some churches encourage the young people to sit together as a group. As long as your teen's behavior is appropriate, there's nothing wrong with that. However, your teens are less likely to misbehave if you've made the expectations clear and they are sitting next to you. Alternately, you could use the privilege of sitting with their friends at church as a reward for behaving appropriately. Ideally, you should explain this to them ahead of time.
Teens crave respect, especially from their parents. Showing them the respect of speaking to them -- rather than at them -- about the behavior you expect at church will often get you farther than any punishment or consequence you could lay on them. If your teen is showing problem behaviors in church, ask him why and hear him out. Often, you can resolve the issues that lead to teens acting out in church by simply talking them through and making the expectations clear.
Often, teens have trouble behaving in church because they're bored and don't see the service as relevant to their lives. Look for things in the sermon that apply to your teens' lives and ask them questions about them after the service. For example, if the sermon was about forgiveness, you might ask your teens who wronged them recently and how they can apply the message they heard in church to those situations. Teens find it easier to listen and behave when they view what they're sitting through as relevant to their daily lives.