I’ve been on these threads for a while and understand that in general, self-studying for AP exams doesn’t do much for you, and there are better ways to spend your time.
However, I believe I have a good reason to self-study an AP Exam next year. I’m a rising junior, and am only scheduled for two AP courses next year—Gov and Lang. My science course will be Honors Chemistry, because there’s nothing else rigorous for me to take, and this is the highest class a junior at my school can take. Strangely enough, last year, I was able to take AP Physics C: Mechanics and AP Computer Science A—these two courses sophomore year followed by an honors science course junior year just doesn’t feel right.
I did exceptionally well in both classes, and I enjoyed Mech quite a bit. I think I have a solid foundation for self-studying E&M—although my Mech teacher doesn’t teach the class, she used to teach it and may have some materials for me. I will be taking the SAT Subject test in Physics, so learning E&M will help me with the SAT and vice versa. An extra AP exam won’t be hard for me to handle because I took 4 APs this year and with E&M, will only be taking 3 next year.
I also plan on going into Engineering/CS. I have no E&M knowledge right now, but it will be important for me to have such knowledge going into these two disciplines. My parents wanted me to learn E&M anyway, but didn’t propose self-studying for the exam.
So, based on this rationale, is it alright for me to self-study E&M? The credit may come in handy down the road, too. I’ll probably sign up for the exam anyway, and if I get too busy I can always not take it.
Is E&M not offered at your school?
If it’s not offered, I don’t see any harm in self studying. If it is offered but only for seniors, wait and take it senior year.
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Side note, many schools don’t let or recommend that engineers use AP physics credit. At D’s school mechanics was integrated into her engineering design course and E&M was combined with optics. (She technically got the credit for graduation requirements but that doesn’t help her in any way).
@momofsenior1 Nope, it is not offered. Academics at my school are pretty uncompetitive and there aren’t many options.
The science progression for “advanced students” goes Honors Physical Science → Honors Bio → Honors Chem → AP Physics C Mech/AP Bio/AP Chem.
I took honors bio over the summer last year so I could take C Mech since I had the math prerequisites, and took APCSA online. As an enthusiastic STEM student, my school offerings just aren’t good 
Remember that no college expects your to specialize as a HS students. Many schools don’t offer E&M. If you are genuinely interested, go for it but if you have AP mechanics and AP chem on your transcript from school, that will be plenty rigorous enough in terms of your science courses.
If you’re interested in the topic, certainly go ahead and learn it. My D has been through a few MIT online courses because she was interested in the topics. Learning is always good.
Just don’t expect the actual AP exam/score to be some advantage in college admissions. Students who think it will be a great thing on their resume/application are the targets of the usual advice.
No harm, as long as doing so doesn’t interfere with your regular classes or things outside of school. IMO, it’s more credible to self study for an AP if it’s of genuine interest, perhaps due to your intended major, and if your school doesn’t offer it. It seems to me you have a legitimate reason.
My D did this back in the day and I think it might have actually been helpful in her situation. Very few students ever did this at her high school. It was notable to her guidance counselor who mentioned it in the letter of rec. The day she took the test, a couple of teachers actually came by the room she tested in, just to see the spectacle, haha.
As far as it being frowned on, I think that’s mostly when it doesn’t fit what I’ve mentioned above.