The success or failure of e-learning courses depends not only on the design and quality of the learning materials but on the ability to motivate students to study them. Motivational factors are of the uppermost importance in e-learning courses since the motivational impact of the student-teacher proximity obtained in face- to-face education is normally not achievable. This paper makes an analysis about how to make use of some of the tools available in e-learning systems to try to motivate students. The paper makes a general review of the available tools and takes a special interest in forums and assessments. The results are validated based on the experience obtained from the teaching of the subject "Internet Society". This subject is offered to the students of all the six public Universities in Madrid (Spain) using a Moodle based e-learning platform. The experience has studied the behaviour of 60 students and their reactions to several motivational stimuli based on forum participation and assessments.