Typical adolescent behavior can sometimes put your child in danger and be an early symptom of trouble. You might be concerned, for example, if you notice your child: Missing classes or entire days of school, training, or job, or lowering one's grades Results are lower than usual, and students are beginning to fail subjects in school. Being obnoxious and hostile to parents, teachers, or other grownups or family members Staying all day and night in the room or online, or isolating from family and friends Not returning home at agreed-upon times