Negotiation surrounds our day-to-day lives. Research in the field of automated negotiations has suggested the design and use of automated negotiators, on one hand to allow facilitation of the negotiation process by human negotiators and, on the other hand to provide automated agents that can negotiate on behalf of humans. Many papers present innovative agents and evaluate their efficacy in negotiations with other automated agents or people. Others focus on building negotiation support systems with the purpose of helping negotiators reach an agreement. Yet. the question still remains whether these systems or agents have the potential of improving people's negotiation skills. In this paper we attempt to shed more light on this topic. By means of extensive simulations with human negotiators we examine and compare several training methods and their implications on the improvement of negotiation skills of human negotiators.