We here at Team 11 are having difficulties with the Tooth Gear Sensor. We are having trouble with the calibrations. It might be because of us not mounting it right, or something.
We are using a fisher price motor if it makes a differance.
Can someone help 
Thanks.
http://www2.usfirst.org/2006comp/Specs/Allegro_Microsystems_Gear_tooth_Sensor.pdf
Make sure your sensor is oriented the way it appears in the pictures, and make sure the air gap is less than a few millimeters.
And you are trying to sense steel gear teeth, right?
The drive coupling on the fisher price is plastic.
Eugene