Authorities said Wednesday that the students involved are all boys, ages 14, 15 and 16. Their names were not released.
The investigation began last month.
Prosecutors say a staff member at Haddonfield Memorial High School found one of the boys using keystroke capture software on a school computer to try to obtain a teacher's password.
That student implicated the other two.
Camden County Prosecutor Warren Faulk says the three intended to change their grades.
They're charged with illegally accessing information.
All three have been released to their parents.
