Children exhibit differences from one another in terms of learning abilities. The differences among most children are relatively small, enabling these children to benefit from the general education program. The learning abilities of some children, however—those called exceptional children—differ from the norm (either below or above) so much that they require an individualized program of special education and related services to fully benefit from education. Modifications in curriculum and instruction are necessary to help them fulfill their potential. Thus, exceptional children is an inclusive term that refers to children with learning and/or behavior problems, children with physical disabilities or sensory impairments, and children who are intellectually gifted or have a special talent.

At risk children are ones who, although not currently identified as having a disability, are considered to have a greater-than-usual chance of developing one.

Exceptional children share certain physical characteristics and/or patterns of learning and behavior. These are:
• Mental retardation (developmental disabilities)
• Learning disabilities
• Emotional and behavioral disorders
• Autism
• Communication (speech and language) disorders
• Hearing impairments
• Visual impairments
• Physical and health impairments
• Traumatic brain injury
• Multiple disabilities
• Giftedness and special talents

* * *

Sources:
http://www.education.com/reference/article/who-exceptional-children/?page=2
http://www.education.com/reference/article/who-exceptional-children/