In this paper we evaluate the effectiveness of an adaptive online learning platform, designed to support Chinese students in learning the English language. The adaptive platform is studied in three studies, where the experimental platform is compared to an alternate, non-adaptive platform, with random assignment to conditions (the adaptive learning platform versus a control non-adaptive online platform covering the same content). The three studies had 39 students, 91 students, and 90 students, all in the eighth grade but in different schools in China. The two conditions were compared in terms of gains on pre- and post-tests relevant to the local schools, as well as on a survey measuring student attitudes towards the technology. The adaptive platform is found to lead to better and faster learning than the non-adaptive platform, as well as more positive responses to survey items.