Most children experience some nervousness at the beginning of a new school year. New teachers, new classes and a whole new routine can leave even the most even-tempered child frazzled and exhausted in the first few weeks. Most of the time, children settle into a routine and quickly work through their early jitters.

For some children, however, normal anxiety gives way to more serious fears. Phobias are common in children. In fact, the majority of specific phobias appear by the time the sufferer is seven years old. Fortunately, most childhood phobias respond well to treatment. Here are some things to look for in children of various ages.
Elementary school
According to developmental psychologist Jean Piaget, children are in the “concrete operational stage” of cognitive development from the ages of approximately seven to eleven. Their fears tend to reflect the concrete way in which they see their environment. Common phobias in elementary school aged children include fears of thunderstorms, animals, and the dark. School-related phobias may also develop, such as a fear of bigger kids or a fear of a teacher that is perceived as “mean.”
Children of this age often demonstrate their anxiety by regressing. They may become clingy, refuse to go into the classroom without a parent and cry or throw tantrums. They may also freeze or run when confronted with the feared situation. Physical complaints such as stomach aches are also common, and usually follow a pattern.
Middle school
Again, according to Piaget, most children enter the “formal operational stage” of development near the beginning of their middle school years. Pre-teens begin to understand abstract topics. And its also a time of immense pressure for many kids, as they struggle to establish their identities, forge more adult friendships and begin to plan for their futures.
The most common phobias in this age group tend to focus on school-related topics. “School phobia” is a general term that may apply to any fears that make the child reluctant to go to school. School phobia is thought to be related to separation anxiety, but may also stem from bullying or humiliation, or a simple reaction to new pressures.
Many kids of this age react to their fears through defiance. They may become argumentative or withdrawn, develop friendships with troublemakers, skip school or even turn to alcohol or drugs. Some children regress instead, becoming clingy and overly dependent on the parent.
High school
High school is a whirlwind time of changes and pressures. Kids of this age are torn between wanting to become adults and wanting to extend their childhoods. They worry about their grades, wonder if they will get into good colleges and struggle to develop adult relationships with their friends.
Agoraphobia and social phobia are most common among this age group. Social phobia can be related to the body image issues that plague many teens. It may be restricted to a single situation, such as a fear of speaking in front of the class, or may be all-encompassing, making teens scared to be seen in public.
Agoraphobia may develop out of an untreated social phobia or another disorder, or may appear alone. Agoraphobic teens may severely restrict their activities out of a fear of losing control in public.
Teens generally display many of the same phobia symptoms as adults. They may refuse to participate in certain activities. They may shake, sweat or show signs of illness before or during a confrontation with the feared activity. Teens may also turn to alcohol or drugs as an escape. They may spend a great deal of time alone, and may gradually develop depression or other disorders.
(Source: about.com)