The best answer I can give you is probably not. I know there is a lot of pressure for high school kids at this point in time to do college classes early, to attend summer camps at universities etc. If you would like to attend a very competitive university with a low acceptance rate (Standford, MIT, Harvard), then it is important to go through experiences that can differentiate you from the rest of the crowd. One of those can be summer college classes, but volunteering, school groups, personal projects can be other ways of standing out.
However, I would say that when you're looking towards colleges you should first focus on your high school academics. There's no point going to a college courses in high school if you don't feel comfortable with the high school material. If you don't have any gaps in your high school education, I would say you should go for it! It will give you invaluable experience and will help your application to the university.
If you care solely about academic performance in college with or without taking prior college courses; I would say that many of my classmates who did not take previous college work in high school and did great in college.
It really depends on each individual however; could a college course spark some creativity in you? is the professor particularly charismatic and you're interested in the topic? does the college course distract you from the summer homework you need to do to succeed in high school?
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Great question! While the answer is different for everyone, generally, most colleges will want to see that a student has taken at least one challenging class in high school so they can better prepare for the kind of study habits and time management needed on campus. I have heard of kids who took the easiest classes in high school so they could have great grades, and then found it very difficult to transition to college because they had never learned how to manage academic challenges.
If you are still in high school, I would say, go ahead and take one challenging class to see how it is for you. You may surprise yourself by realizing it's not as hard as you thought. Or maybe, you will learn that while the subject matter is more challenging, you found a great way to manage your time and keep up on homework to still get a grade that pleases you. Even if you find you didn't do as well as you hoped, there are positive things that can be learned from that. Perhaps it wasn't an easy subject for you, and that is good to know before going to college. Or, maybe you did not put in your best effort. Again, this is something you can change the next time you have this experience and that is all a part of learning. These are the kinds of lessons that are learned by us only when we step out of our comfort zone. Good luck!
I hope this helps!
Best of luck!