Answer:
Attention deficit hyperactivity disorder
Step-by-step explanation:
Attention deficit hyperactivity disorder (ADHD) is a mental disorder which makes people unable to focus on something for a given span of time. This is compared with the amount of time a person which does not have the disorder. If it does not match then the person is diagnosed with the disorder.
Here, Jacob who is 9 years old cannot put as much mental effort as the other kids in his class can. This causes him to lag behind in schoolwork and homework.
Hence, Jacob has met one of the criterion of ADHD.