I agree with Ramjet that it depends on your attitude. There is not one flight school that will 100% guarantee an instructor job after you do your instructor rating there. I am a foreign student who is attempting to start my flight training at Harv's soon (depending on whether I'll get a visa and when I get it because of the diplomat strikes) and from what I've heard and read around, they hire a good number of the instructors they train, and also it completely depends on your skills and attitude towards flying. And you should also know that from what they say, they only hire the instructors that they themselves train. So I guess you will have to deduce your own conclusion from this information.