A great deal of research explores how implicit vs. explicit instruction affects second language learners' grammatical accuracy, generally finding that explicit instruction increases accuracy. However, no research to date has examined the impact of implicit/explicit instruction on learners' fluency. Additionally, nearly all the research has only tested adult learners, despite strong claims about the effects of age on implicit vs. explicit language learning. This study tests the impact of implicit or explicit training on children's and adults' performance with an artificial mini-language. After seven days of training, fluency, accuracy, and explicit knowledge were measured. Implicit groups became significantly more fluent than explicit groups. Adults were more accurate than children, but training condition did not significantly affect accuracy. Adults and explicit groups developed more explicit knowledge than children and implicit groups, with no interactions between age and training condition. This study is one of the first to show measurable benefits for implicit second language instruction over explicit instruction: both children and adults produce sentences more fluently after implicit instruction.