This study investigated the motivation of a heterogeneous group of students studying English as a foreign language at the International School in Tripoli area. The aim of the study was to find out the extent to which various factors affect students' motivation and achievement in second/foreign language learning particularly as they enter the senior high school. The research also looked into the temporal dimension of L2 motivation to see if the students' motivation changes as they enter the senior high school. One hundred and forty four students from thirty five nationalities learning English and five teachers participated in the completion of the questionnaire surveys. Twenty students and three teachers took part in the semi-structured interviews. Data were drawn from students' examination results and a combined quantitative-qualitative approach in which student and teacher questionnaire surveys were followed by a round of student and teacher interviews. The results of the "Student's Motivation Questionnaire" show that L2 motivation in the sample decreases with age: The results of one-way analyses of variance across the five age groups investigated show that the older learners tend to score significantly lower on the motivational scales and the interviews data gives further support to this finding. There are a number of influential factors that affect learners' motivation: in particular the role of the teacher was seen fundamental in determining the attitude to the language and in supplying motivation. Other external factors include aspects related to the learning context.