How to practice riding a motorcycle?

Hi I'm currently 18. I want to get a sports bike 500-600cc either Kawasaki Yamaha Suzuki or honda in that order depending on what I like. But I want to master riding before hand.
I took the motorcycle training course sadly I failed the evaluation. I'm terrible at slow u turns which I wish I had enough time to practice on. I asked for help on how to master it, they weren't that helpful. Or I'm just that terrible of a student but I'm willing to work on it and retake the evaluation on a different date but I want practice. How can I? I live in California so I can't even get a permit without completing the class. I don't know anyone with a motorcycle I can't rent one. I'm even willing to buy a dirt bike to practice. Is there anything I can do to start practicing?

I think you hit on the best idea. Get a small to medium size used dirtbike and go do some riding in the countryside. All bikes work and handle about the same, and even on a light little dirtbike you'll learn what can get you in trouble and what not to do on a much heavier street bike.

It's like riding a bicycle, only faster, and you have to get a feel for working the clutch and shifting. If you have not ridden a bicycle for a while, maybe get a mountain bike, practice on that including slow maneuvers. Then get a dirt bike and master that.

Note that on a motorcycle you get a good view of your surroundings, but need to keep "aware" of your surroundings and drive defensively. In other words expect the unexpected because other drivers may not see you or may misjudge your speed.

You mention both a dirt bike and a sport bike.

The dirt bike is built rugged, has a low center of gravity, is light weight, and has easy forgiving handling.

The dirt bike's polar opposite is the sport bike, heavy with a high center of gravity, tweaky handling, comes with fragile easy to snap off shift and brake petals, covered with difficult to repair, and expensive to replace fragile plastic panels.

What bike do you wish to learn on?

Hay bud, someone mentioned bicycle practice that for slow maneuvers, you'd be surprised at the similarities, minus the clutch and how the breaks react, take the class over but honestly i gotta say if you don't pass the class that does not mean its unfair, they are trying to save you, practice and get comfortable first, i passed the class had countless close calls, even hit a guardrail going 30 something, because i chose to ride before i practice, going in a straight line is something anyone can do, slow - med speed turns is what will get you.

A sport 600 bike is a great way to kill yourself if you can't even manage slow U turns yet. Leave it as a dream for at least 3 years. By all means get a smallish dirt bike & practice. Mountain bike riding is cheaper & healthier for gaining the basic 2 wheel skills. Once you pass the test go for a LAMS approved bike - lighter & smaller is much easier to pick up after a drop. Second hand is best as you WILL drop it.

If I were you I'd buy a Dirt Bike to practice on. 1. They tend to be pretty cheap. 2. If it falls over or you lay it over while riding more then likely it isn't going to damage it. I myself have a 2009 Honda CBR600RR an it was my first sportbike also. But I have rode dirt bikes since the time I was 8 and I'm now 21. Having a dirt bike will allow you to become use to shifting and using a clutch if you aren't use to it. Keep in mind that different bikes have different clutch release times so when you do go for the class again just slowly release on the clutch to find it's engauge point. You'll get the hang of it, it really isn't tht hard. Best of luck.