Dear Ms. Voisine,
Symptoms of Attention-Deficit/Hyperactivity Disorder (the correct name for the condition) cluster in three areas: inattention, hyperactivity and impulsivity. Some children display symptoms in all three clusters, some children in two of the three clusters, and some children display symptoms in only one of the clusters. So, the range of possible symptoms can vary greatly.
In addition, the degree of severity of the symptoms can also vary greatly, from mild, to moderate, to severe.
And, while it is correct to say that most children who display ADHD manifest some difficulty in their ability to attend to some subject matter in school, it is not necessarily true that a child with ADHD will have problems sustaining attention in all subject areas. Even children who display ADHD can attend well under conditions of high motivation.