How can you make your dad let you join JROTC?

Make isn't the issue. Convince is. See the instructor, do up a list of pros and cons and sit down with your dad.

JROTC couls well be a step toward a long career in the military. I agree with LTC Brown that you should be getting a list of pros and cons and maybe schedule appointment with school counselors, your dad, the JROTC folks and yourself. Be positive about it and, I am saying this as a parent, listen to what your dad has to say as well rather than getting upset... remain calm and show him you are responsible and mature enough to handle whatever additional load JROTC will involve..good luck

First, you're a kid, you don't "make" your parents do a damn thing. Second, what is your parents' objections to the JROTC program? Lastly, perhaps you should just sit down and have a discussion with your parents instead of asking pointless and unanswerable questions to a bunch of adult strangers on the internet.