Do you have to get good grades to be in the marine core?

Yes. To be in the Marine Corps you must be between the ages of 17 and 29 and are working toward, or have earned, a high school diploma to qualify to enlist. Now to your question, 'Do you have to get good grades to be in the Marine Corps?' If you have to have a 'High School Diploma' to be in the Marine Corps then you must have passing grades to graduate from High School. The better the grades will help you get a high score on your ASVAB Test (Armed Services Vocational Ability Test). Combinations of scores from the nine tests are used to determine qualification for a MOS (Military Occupation Specialty). Normally the better the score on the ASVAB Test the better the job in the military. So do your best to get good grades in High School.