Yup,
Like the last post said, listen to your instructor. Things may have changed at your field (taller grass, your nose gear may have bent back slightly, etc) since you first started learning there. Even though you have a tricycle geared plane, the drag of tall grass, too small a nose wheel, or slightly bent back nose gear can all cause the nose of the aircraft to assume a slightly "negative" angle of attack as you try to accelerate. This "digging in" so to speak, of the nose can at the very least cause so much drag that the plane stops accelerating before you have suficent safe airspeed to rotate and lift off, and in the worst case, (I've seen it happen with a soft/flexible nose gear) cause the prop to start mowing grass (big time power loss) instead of lifting the plane off.
As another poster above said, what your instructor has described to you is a soft field takeoff procedure, also used in some full scale planes. If you think about it, by holding less pressure on the nose wheel (up elevator), or even holding it slightly off the ground, there is MUCH less ground drag (1/3 of your wheels are almost or totally off the ground). This keeps not just the nose wheel, but also the prop well clear of the grass and allows you to accellerate the plane faster and also achieve a HIGHER ground speed, than when you were "plowing along" with a negative (nose down) attitude.

With this said, it is true that you should slightly reduce the up elvator as the speed increases so that you do not lift off too soon into a stall, so this type of takeoff DOES make you think a bit more than what is described in your planes manual. Also, you MAY be able to accomplish something similar by just going to a slightly larger diameter nose wheel that holds the nose at a slightly positive angle of attack, but then you will also still have to have enough power on hand to handle the drag of the nose wheel in the grass on the takeoff roll.

Hope this all helps,

Lee