You should be working on placement files around your junior year, which will most likely include references from college instructors. But, except for methods classes, they won't have much of a judgement on how you will act in a classroom. Also, you want your student teaching experience to be positive, and having some sort of experience with youngsters ahead of time will help in that avenue, too.
Where can you get this experience? For one thing, see if you can find the time to give lessons in your particular area. Often, colleges will have "prep" programs for students and instructors to give lessons to outside clients. The college will collect a percentage of the lesson cost and pay you. Of course, you can't set your own price, but changes are good you'll end up with good students. This will help you get involved in music festivals and other performances you'll likely encounter as you start your teaching career.
If you have enough college hours, consider becoming a substitute teacher. At least in Missouri, college holidays don't always exactly coincide with K-12 school schedules, so you can get in some days during your winter or spring holidays. Sign up at your home district or at the district where you attend school. This is a super place to see the "real world". Substitutes have to be on their toes constantly and establish assertive authority in a matter of minutes. What a great way to build up your discipline! You can also pick and choose the days you go in (but be careful: many districts won't call you back if you turn them down too often.) Finally, substituting will give you insight of what will be going on in a student's life beyond their music classes. If you do this, make sure you get support from the principal, and walk in with your own bag of tricks. Most teachers are very good about being prepared for a substitute, but some aren't! There
