I respectfully disagree. There ain’t anything close to real Physics in that course:
https://apstudent.collegeboard.org/apcourse/ap-environmental-science/course-details
btw: it may have low pass rates due to self-selection. The vast majority of top STEM students don’t take it. OTOH, the “less strong” science students take it instead of AP Bio or Physics, just as they take Stats over Calc.
S2 took APES as a sophomore. The pre-IB Bio (honors, intense) he took in 9th grade was excellent prep. He took pre-IB Chem as a soph as well, which dovetailed nicely. He was also seriously into environmental sciences at that time and has an interdisciplinary bent, so the course worked well for him. He was the only soph in a class of seniors who were taking the course as a SL Environmental Science course under the IB program. Got a 5 on the AP exam without doing more than the regular assignments.
He took AP/IB HL Bio senior year and got a 5 on that AP. The overall IB program requirements made it hard to squeeze in extra AP science courses. IB HL Physics at his school was a two year course; HL Bio was a double period, and only SL Chem wasn’t offered. He had semesters where every class was an AP or IB. Insane.
Our school does do multiple blocks for advanced English, Math, and Science courses–typically it is two blocks every other day and one block the others.
S has decided to stick with the honors science track and leave the AP stuff until 11th or 12th grade. He has enough to deal with as a freshman with honors classes, cross country, and his first season of marching band!
Thanks for all the input, and hopefully this can help someone else in a similar situation.
Excellent choice. Best of luck to your S.
Only if he is personally interested. I would not encourage class like this but NOT FOR the reason that it may be difficult, I cannot imagine that it is difficult…
My S did this: Freshman…Honors Bio.
Soph…APES and Honors Chem.
Junior…Honors Physics
Senior…AP Bio.
I know everyone seems to be saying that freshmen won’t be ready for college level courses, but unless APES is astronomically different at your school OP, at my school APES is practically a regular course. I’m taking it now (I’m a junior) and I have 3 other APs as well- AP Chemistry, AP English Language, and AP US History. APES was by far the most manageable of all of them if you stayed on top of it, which I’m sure a smart guy like your son who only has one AP would be sure to do. I received an A both semesters (well it’s looking that way for this semester anyway! our finals just got put in but I’m not sure if anything else has to go in or not), but will not be taking the AP exam that is actually tomorrow. It had nothing to do with not knowing the material though, it was just that AP Chemistry is at the exact same time as the APES exam and although you can take both, I didn’t want to deal with the hassle honestly. Lame excuse I know, but I really just wanted to focus on AP Chemistry tbh.
I think it’s 100% feasible for a freshman to take APES. It’s not hard material at all- it’s all memorization. The reason the APES exam has such a low pass rate is you really have to take into account the types of students who take APES… it’s always considered the lightest of all the APs at almost every school (besides maybe psych) and therefore students who generally do not take AP course load take this class as their one and only AP. That’s by no means a bad thing, but generally those students are not prepared to pass an AP exam because for the most part they are more underachieving. I just know that the student demographic in my APES class is WAY different from any of my other AP classes- a lot of kids you wouldn’t expect to be taking an AP are in APES, so it’s for sure a lighter AP.
Then taking AP Bio as a sophomore sounds like an excellent idea, it’s mainly a sophomore class at our school, although I did end up skipping it sophomore year and will be taking it senior year. Oops. 
AP Chemistry is a fantastic course if you have a great teacher, but honestly, don’t take it any younger than junior year. There’s students in my class taking it freshman/sophomore year and they really set themselves up for failure. They just don’t have enough math background or high school experience yet to be able to handle AP Chemistry- it’s by far the hardest AP I’ve taken thus far, and probably will be the hardest one I take. I still loved the course, and am just praying I pass the exam tomorrow morning, but if your son takes it… make sure he knows what he’s getting into.
Overall in this essay I just wrote I just wanna say that APES as a 9th grader imo would be a great intro to tougher AP classes. I know many parents here are against it, but speaking as a person who’s actually taken the course and as a person who’s known to be very lazy, it’s really not bad at all.
If the kid strongly wants to take APES then let him. If he is unsure then he should not. He should have a strong critical reading skill to take it. My son took Honors Bio & AP Bio (block schedule) in 9th grade because he said he did not like biology and wanted to get over with it. He complained the teacher went too slow in class and he aced the class.
Strategically I think your son should take honors bio to prepare for AP Bio or AP Chem in 10th, 11th grade. He can easily take APES later after honors bio. He needs some easy AP class in 10th, 11th, 12th grade. But he should not to take APES after taking AP Bio because he needs a balanced curriculum.
My school doesn’t offer AP Environmental Science but AP Bio and AP Chem can only be taken senior year by those who have already completed physics(AP or regular).