Jump lesson - Duke still spicy

Tonight we jumped in a solo lesson, but Duke was still grabbing the bit and rushing at the fences.
John had me half halt, bend him to the outside, steer him (both hands) to the inside, and halt after the fences.  We jumped little fences, and John had me kind of sneak up on them, but once Duke caught on we were jumping, he was still an eager beaver.
It was a good lesson to work on riding him, but it was kind of frustrating that we're still struggling with this.  I'm not quite sure what's going on.