Subject Tests after Junior Year

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Take Math II for sure. I wouldn't suggest taking the US history subject test as you want to have a science-related major, and sadly, history is unrelated for the most part unless you're a history or humanities major. I have to say that it would be more beneficial to take one of the biology or chemistry subject test, although you would probably score higher after taking their respective AP courses. If you are only comfortable taking Math II, just take Math II. Take one of the science tests if you study extremely hard for it (buy a review book, Khan Academy AP practice).

However, I would like to emphasize that almost all schools during this time are no longer requiring/recommending subject tests, and they will have less of an effect on your admissions profile. Look closely at the colleges that you are planning to apply to and evaluate whether you still need to take these tests. If you don't believe that you will do well on the tests, don't take them. I personally would not study ridiculously hard for a subject test that may not have a great impact on my application when I could be focusing on other aspects of my application that may be of greater value.