When someone has ADHD, they have extreme problems with ......

Attention

People with ADHD make negligent errors. (e.g. they know that 5+5=10 but they would write 11). Children who have ADHD have problems with attention in class. (e.g. they would day dream). When you talk to a child who has ADHD it seems like they don't listen to you even though you are looking straight at them. They don't usually follow instructions/directions. Children with ADHD have problems with organization, also they usually lose their things like toys, pencils, books, etc. They're also distracted very easily by other things and they forget their things for daily activities.

Controlling Impulses 

In school, if the teacher asks what is the answer for a question, a child with ADHD would probably yell it out with out giving the other kids a chance. They usually budge in front of other kids in a line (in other words they can't wait their turn). Also, if their mom/dad was on the phone they would probably interrupt. 

Hyperactivity

Children with ADHD play with their hands, feet and often move around in their chairs. They also usually don't stay seated when asked to and they run and climb about. They have a lot of trouble with silent activities and they talk constantly.