Subject tests should generally be taken after you have finished the highest level classwork related to that test. While that is nice in theory, the reality is that you need to have these tests taken by fall of senior year which means that you need to have taken the classes by end of junior year.
You also don’t want to wait too long to take the test after you have the course work so late spring of junior year makes sense. Maybe.
The problem with testing the late spring of junior year is that this is the same time that you should have completed your SAT and most students will also have a number of AP tests to take at this time.
To further complicate the matter, you can not take a regular SAT and the SAT Subject Tests on the same test date. So, you are left with three SAT test dates between March and June of your junior year and you need one date for the SAT and one for the SAT Subject Tests. You can take the third date for a second SAT but that makes for a very busy spring.
And if this all isn’t starting to concern you, if you take three Subject Tests on a test date but are concerned that one of them didn’t go well, you can’t just cancel the test that didn’t go well. You either keep all of the tests from that test date or you cancel all of the tests from that date.
Ideally, you will get your SAT Subject Tests done before spring of junior year so that you don’t need to worry about them at that time. If you can get your courses taken early then you can take the Subject Tests early. This takes careful planning throughout your high school career.
Help with this type of planning is a common reason why families hire admission consultants. Do you need help?