It's possible that your child's challenging behavior comes from a sense of uncertainty. During the young adult years that directly follow high school, adolescents may struggle with the transition from childhood to independence. You need to give your child some space -- even if she's still living at home -- to feel like an adult according to the American Academy of Pediatrics' HealthyChildren.org website. Consider the possibility that she's acting out when she has her own full-time job and is ready to step out on her own because you're still coddling her like a child. Offer advice and help if she needs it, but allow her to act like an adult. This may mean that you lift her curfew or ask her to contribute financially to the bills.

Your child's new adult status isn't an excuse for acting in a disrespectful way. Whether your 18-year-old lives with you or not, he still needs to show the same level of respect for you and your rules as he did when he was younger. Talking back to you, arguing or ignoring your family's rules isn't acceptable -- at any age. As the parent, it's part of your job to tell your child when he's out of line, according to psychologist Linda Sapadin on the website PsychCentral. Know that there's a difference between defiance and your child expressing his opinion. Make a stand and tell your teen that you won't tolerate rude or disrespectful behavior. If it persists, sit down and discuss what the problem is. Maybe he feels like you're babying him or he's scared about what the future holds.

Challenging behaviors don't just include defiance or angry types of actions. When your high school grad suddenly seems depressed, you need to know how to handle this potentially serious situation. The American Academy of Pediatrics notes that excessive sleeping, extreme moodiness and a noticeable change in personality are all signs of depression. Talk to your teen to make sure that what you're seeing is just her being tired from late nights out with friends or working hard at a new full-time job. If you suspect that your child is depressed, consult an expert. In the event that your now-adult child refuses to see a therapist, you can consult a mental health professional yourself for professional advice.

Your 18-year-old whines when you don't make his bed, can't seem to put together a meal for himself and expects you to pay for everything. If your child's challenge is his immaturity, you can deal with this behavior by not catering to his each and every whim. Instead of handing out an allowance, acting like his personal chef and doing his laundry, start treating him like an adult. This doesn't mean that you have to completely cut him off. Rather, stop acting like he's still in preschool. If you're going out with friends, let him make his own dinner or ask him to go grocery shopping -- and pay for the food on his own.