Hello!
I am a junior on the cusp of the college admissions process! I had a question: in terms of teacher recommendations, should I ask 3 or 2? I have already asked my English and APUSH teacher, (both agreed) however, I plan on applying to a lot of privates (20? might seem like a lot and not enough college research, but hey, everyone has their own journey), and I was wondering if I should ask an extra teacher (my science teacher) to split the workload. Even though teachers can send the same rec to all schools through Common App, will they be annoyed if you apply to a lot of schools, and thus they have to do more work (personalizing letters, sending through other means for schools that don’t take Common App?) Please give me insight ASAP bc I have to ask my science teacher by tomorrow! 
Thank you very much!
You should not submit more rec letters than a college asks for. If a college allows an optional third rec letter, ideally it should be from someone who can shed light on you that a teacher can’t: a boss, coach,pastor, or other person who knows different aspects of you.
At my kid’s high school, you are only allowed to ask two teachers, and you can’t see the letters. No teacher is going to personalize 20 different letters for you, sorry. Asking a third teacher may just annoy the other teachers. Rec letters are a lot of work, and ideally you want them to come from the teachers who know you well, who like you, and who you also like. I assume the two teachers you asked fit this bill. It’s fine to ask them to mention a couple of things in your letter, but it’s not fine to ask them to customize letters for twenty schools.
They shouldn’t need to anyway. The point of the rec letter is to give insight into who you are as a person. They want to see beyond the stats and ECs. If you are a person who asks teachers to rejig a rec letter for every different school, I do not think that’s going to please anyone. You need to think about what you think the teachers are going to say about you. They should not have to change anything just because you plan to apply to a bunch of different schools. And, unless you are planning to compare FA offers, twenty schools is way too many, IMO. Twenty apps doesnt equal twenty lottery tickets.
For the most part they will write one LOR and it will go out to all schools. If all the schools you are applying to are on the Common App, it is as simple as that. Does your school have Naviance or something like it? The teachers upload the letter once and that is it. The GC will release the letter as needed and the teachers have no idea how many schools you are applying to. For the most part even if you have schools off the CA the same letter will be used and the GC can still take care of it for you.
There are some schools that do require an individualized letter through their own portal-MIT for one but I don’t know how many others there are. MIT also required S to solicit a 3rd recommender because he was using a science and math teacher, but MIT requires a humanities LOR.
Where is really gets tough is the scholarship LORs. Those all need to be personalized for the specific scholarship and unless you have a close relationship with a recommender it can get tough to keep asking. Many scholarships only require one LOR and you can rotate between teachers, or many allow the letter from the GC or even an outside recommender like a coach, employer, etc. so if you are applying for a bunch of scholarships you can spread the letters around. My kids found it very stressful to keep asking for the LORs and I don’t know how some kids manage to apply to like 100 outside scholarships?!
I agree, everyone does have their own journey and plenty of kids apply to 20 schools.
Just because plenty of kids apply to 20 schools doesn’t mean it’s a good idea.
The teachers will write one letter. Even if the school has a slightly different format, most teachers will still just use the letter they wrote for the Common Application. I don’t know if there are other schools besides MIT that ask for both a science and non-science recommendation, but that’s the only reason I know of to bring the science teacher into the mix.
You should tailor your applications to the schools while still being true to yourself. It’s very difficult to do a good job of this for more than a dozen or so schools.
Writing supplemental essays to 20 schools are much more work than a teacher writing the same letter for 20 schools. If your “why this school” essay can be shared among multiple schools, then it is a generic one that no adcom likes.
Agree with @Lindagaf If you submit a third recommendation it should be a supplemental recommendation from a person who knows you outside of the academic world (ex. a boss, club advisor, clergy etc.). And in terms of asking the science teacher, you should only do so if a school requires a STEM teacher LOR, otherwise it is wasting his/her time. You need to respect the fact that teachers write the LORs outside of the school day on their own time. Letters will not be personalized by school so don’t even consider that as an option.
In terms of how many schools you apply to that is your decision entirely. My only caveat is that each application, particularly the ones with supplements, takes time and energy. Don’t sacrifice quality for quantity in preparing supplemental essays.
Hi all, thanks for your guidance! It has been immensely helpful 
I’ll stick with the two teachers I have now.