I have tried using the Hi Technic Compass Sensor in my classroom, but was not able to get repeatable results. The same position in a grid would give different readings. Does anyone know if the Dexter dcompass may work better for me or if there is another sensor that I should look at to get a reliable compass reading? Thank you.

If there is metal in the sensor surroundings (steel building etc.) it could severely effect the readings. It's also recommended that you calibrate the compass on the robot, and in the environment that you will be using it with. Something that is also required, but occasionally forgotten, is that the compass needs to be a minimum of about 15 cm away from the NXT, motors, or any other sensors.

The differences between the dCompass and the HT Compass are irrelevant if the readings are being improperly effected by it's surroundings.