It's a matter of time and training. Yes, cats ARE trainable! I know cats who only go outside on a leash. We live in a city, and while it is suburban-like in some places, the roads are very busy. After a while, she will associate the leash with - "Oh, good we're going outside!" Maybe make a routine - each day you take her out for a while when you get home from school or something. Go for a walk with her, even. It's nowhere like taking a dog for a walk, it's more like meandering about in a general direction, but it's fun for kitty!
