A Training Level horse must be on the bit; he must accept the bit and maintain a steady contact on both reins. However, it isn't required for his head to be completely perpendicular to the ground (on the vertical). It is as great a fault to be behind the bit as to be above it. The horse must step with equal energy in both hind legs towards the bit, thus lifting his forehand with every stride and lightening the pressure on the reins. His throughness can be improved by taking on the reins (half-halting), and then giving, asking him at the same time to engage behind and step more into the bridle.
The young horse's frame will be longer than a horse at a higher level, who is expected to have developed a measure of collection, but he must show at least the beginnings of self-carriage. He must not lean on his rider's hands for support, but he can use them to a certain degree to help balance himself. Each transition and half-halt will shift his weight momentarily onto the haunches, strengthening them and suppling them, and at the same time, improving his balance. He must also be instantly obedient to the rider's rein, leg, seat, and spur aids, if not, the whip is there to remind him.
At Training Level, the horse should be able to bend equally to both sides on a 20 meter circle, be more or less straight in his body, which he should be if he can bend equally to both sides, begin to carry himself in balance, maintain an even contact on both reins without resistance, be relaxed in his back, exhibit correct gaits and rhythm, and be obedient. Without these prerequisites, there is no foundation upon which to build.
One must remember that proper contact and head carriage is a result of relaxation and suppleness. Forcing the horse into a frame will not further his development in dressage. When the horse is both laterally supple (achieved by bending to the side, as on 20 m circles, etc.) and longitudinally supple (achieved with transitions and half-halts), then he will relax onto the bit of his own accord. When the horse stretches onto the bit, which can be tested with the exercise "forward, down, and out," then the first step has been taken towards the development of proper contact. The horse's back will swing more freely, and he will suddenly feel more energetic in his haunches - it is as though he has breathed a sigh of relief.