Teenagers can be very unpredictable with their actions as they learn to adjust to a learning period in which they are becoming adults. Sometimes a dramatic change in their behavior along with strong feelings of independence can make them appear to be negative, especially to their parents and other adults. It is important to understand if the signs are normal or if there is a serious, underlying problem.
Discipline
If you notice that your teenager suddenly is becoming out of control and shows a great deal of negativity toward you as a parent it could be due to lack of discipline. Discipline is important with teenagers and helps to set boundaries. Parentingideas.org explains the three R's of consequences in teens: reasonable, respectful and related. An example of reasonable consequences includes disciplining him based on his negative behavior by making the consequence within reasonable means. An example is losing driving privileges for a day instead of an entire month or unreasonable length of time. Respectful refers to giving him firm discipline but in a respectful way without hurting his self-esteem. Related means disciplining him based on what he has done wrong or his negative behavior -- remove him from engaging in a privilege related to the action.
Mental Health
Some teenagers who are negative toward their parents might be suffering from an underlying mental health issue. One mental health issue that can spark negativity is a personality disorder, notes MayoClinic.com. If she has a personality disorder she might display an unhealthy way of thinking and behaving toward you as a parent and teachers at school. Her actions could be negative and she might blame you or others for her problems and feelings. A psychologist can diagnose a personality disorder and help her establish a positive outlook on life through behavioral therapy and individual counseling sessions.
Physical Health
If you see a sudden change in your child's behavior, especially a negative one, it could be an indication that he is suffering from some form of substance abuse. Substance abuse can involve drugs and alcohol and can often generate negative and angry mood swings. There could be several reasons your teen abuses drugs or alcohol, including to soothe stress levels or the effects of an undiagnosed mental illness such as bipolar disorder, explains the Adolescent Substance Abuse Knowledge Base.
Bullying
Teenagers who are suddenly negative or act outside of the normal range could be the victim of a bully. Besides negativity, she also might seem anxious, drop out of her usual activities, have a change in friendships and begin to miss or skip school regularly. When confronted, she might try to deny being bullied and not want the bully to get in trouble to prevent retaliation and ridicule. Speak with her teachers, principal and counselor about how to resolve a bullying issue with his peers; do not try to handle the situation alone.


