We investigate whether peer effects at work differ by gender and whether the gender differencein peer effects –if any- depends on work organization, precisely the structure of social networks.We develop a social network model with gender heterogeneity that we test by means of a realeffortlaboratory experiment. We compare sequential networks in which information on peers flowsexclusively downward (from peers to the worker) and simultaneous networks where it disseminatesbi-directionally along an undirected line (from peers to the worker and from the worker to peers). Weidentify strong gender differences in peer effects, as males’ effort increases with peers’ performancein both types of network, whereas females behave conditionally. While they are influenced by peersin sequential networks, females disregard their peers’ performance when information flows in bothdirections. We reject that the difference between networks is driven by having one’s performanceobserved by others or by the presence of peers in the same session in simultaneous networks. Weinterpret the gender difference in terms of perception of a higher competitiveness of the environmentin simultaneous than in sequential networks because of the bi-directional flow of information.