Select a teacher from a core academic course in your junior year. Or, if you feel that you have a strong rapport with a teacher in a class you really enjoy in your senior year, it might make sense for you to ask that teacher. If you are applying Early Action, however, you’ll want to feel comfortable enough and have enough coursework completed to be able to ask the teacher by Oct. 1, so that he/she has enough notice and time to write a letter on your behalf.
If you are fairly set on applying with the intention of majoring in math, science or engineering, we highly recommend that at least one recommendation letter is from a math or science teacher.
If you are having a difficult time choosing who to ask, think about who comes naturally to your mind when you think of the courses you had last (or this) year.