Most students take AP classes during their junior and senior years, but if you feel comfortable taking AP classes during your sophomore year and have completed any prerequisites, go ahead and take them. Talk to your academic advisor to make sure that you meet all requirements—some schools require certain GPA levels or prior honors classes.
Deciding when to take AP classes depends primarily on your academic schedule. If you plan to take several AP classes along with prepping for and taking the ACT and/or SAT, you need to be aware that you might be stretching yourself a little thin, since your tests are likely to occur around the same time.
It’s important to note that AP classes you take during your senior year will not affect your admissions process, other than showing colleges that you are willing to continue to challenge yourself. However, the scores you receive on your exams can influence placement in college courses and can even result in college credit, so don’t slack in AP classes and exams during your senior year.