"WhatsApp" is a potentially influential informal learning tool that may be used on the go. This study examines its potential utility in EFL writing with special reference to gender. The treatment encompasses a "WhatsApp"-based instructional program designed specifically to help develop writing performance, along the aspects of "content and ideas," "organization and mechanics," "vocabulary," and "language use," among 98 Jordanian eleventh-grade students. The participants were divided into two experimental groups, one male and one female, taught through "WhatsApp." The data were collected by means of a pre-/post-test whose analysis revealed improved writing performance, more for female participants than for their male counterparts.