This article reports the findings of a controlled quasi-experimental study investigating the effects of motivational strategies on learner motivation and achievement in English language classes in Saudi Arabia. The study was conducted in two stages. In the first stage, the most important motivational strategies were identified. In the second stage, 437 learners divided almost equally into two groups (experimental vs. control) and 14 English as a foreign language (EFL) teachers were recruited. Motivational strategies targeting the situation-specific motivational disposition of learners were implemented in the treatment group for approximately 10 weeks. Three instruments were used to assess teacher motivational practices and learner motivation levels before and after treatment. Learner achievement was measured three times during the study period. Statistical analyses (e.g. analysis of covariance and mediation analysis) were used to evaluate the study findings. These findings revealed that the motivational intervention in the experimental group led to increased learner motivation, which in turn led to higher achievement levels for learners in the experimental group than for those in the control group.