ISO: Can't make my pita puff

Hi, I have a recipe(given below) for Arabic pocket bread (pita). I endded up with 12 pitas and of all of them only one puffed up beautifully and looked liked the real "McCoy"(and for the life of me I don't know how I managed it). The others were just plain flat breads.
Now, my question is how do you get pitas to puff up and make a pocket? Since I got one of them to puff up; then that means the recipe is good.
The recipe said to put the oven on 375 but I put it on 475 and I used tiles.
What makes the pitas to puff? Is it the heat?
or is it the way you flatten them? Or what?????
Please help!!!

Here is the recipe for anyone who wants it

1 1/4 c warm water
1 pkg. active dry yeast
1/2 T salt
3 C all-purpose flour sifted
1 T vegetable oil

Mix salt with flour in big bowl.
dissolve yeast in water.(I added a pinch of sugar)
Add water, yeast, and oil to flour and mix(I had to add a little more water).
Knead dough 15 min. Let rise 1 hr.
Punch dough and make 12 balls.
Cover balls with a dry towel and let rest 5 min.
On a floured surface, open each ball into 6 inch circle with a rolling pin.(didn't say if we should let the circles rest or not so I didn't)
bake in a preheated oven for 10-12 min.

Note:If your oven is hotter then remove faster.

Good luck!