A learning disability (dyslexia, dysgraphia, processing disorders, etc.)
A behavioral or mental disorder (ADHD, anxiety, panic attacks, depression, bipolar, etc.)
A sensory processing disorder that makes school an overwhelming experience
Having a low IQ
Chronic health issues (asthma, diabetes, congenital heart problems, obesity, epilepsy, cerebral palsy, cystic fibrosis, AIDS)

There are five basic human needs that, when missing from a character's life, could motivate them to pursue this goal. The following needs are all possibilities, but only one of them should be the primary driver for any given character. For more information on the relationship between human needs and outer motivations, please see​ this ​Character Motivation tutorial.

Self-Actualization: Long-term disorders or illnesses can change a person's focus so most of their time and energy is just focused on getting by. This leaves little time for one's passions. If a child's desire to become self-actualized becomes important enough, he or she may choose to come to grips with their problem.
Esteem and Recognition: Most people without a chronic disorder or illness lack true understanding of the ailment or what it means to live with it. This can lead to misunderstandings, prejudice, and fears targeting people suffering in this way. If the sufferer feels a lack of respect from others, they might pursue this goal.
Love and Belonging: A character may choose this goal if they feel a void due to their ailment, such as not being able to make friends or feeling unloved by family members.