Persuasive Technologies (PT) are computational methods, strategies, and design techniques, grounded in social psychology to change user attitudes/behaviours. PTs have been applied in diverse areas, such as eCommerce, health, workplace, vehicles, urban and ambient environments. A kind of PT that has become popular in eLearning is known under the name "Gamification" -- introducing game mechanics (such as points, levels, badges, leaderboards) into non-game environments. We implemented three persuasive strategies in an online learning environment supporting a University class to encourage more active engagement of students in their online learning activities. The paper presents a controlled study that shows a positive effect of the persuasive intervention on student engagement, measured by the increase in their online activities. The study results also show that personalizing the persuasive strategies to the receptiveness of individual students amplifies their effect on engagement.