The interior of the Icelandic Horse's mouth generally has a low palate and sensitive bars. It is beneficial to start them with sidepulls, lindells, bosals, hackamores, rope halters, regular halters, or any other bitless configuration that is not severe.
Young horses have many changes going on in their mouths until they are mature adults. Teeth are still coming and going for a while. Training bitless saves them from discomfort from the bit.
The horse should be trained with emphasis on relaxation; no tension on the reins, so that the horse can relax his head and neck.