The promotion of an active lifestyle has become a priority in Western societies and school plays a dominant role. The primary objectives of this thesis were i) to examine the lifestyle and physical activity (PA) patterns of a sample of Greek children and ii) to examine the applicability of a school based intervention programme in promoting PA and sport participation. For the purposes of this study the Physical Activity and Lifestyle Questionnaire (PALQ) was developed and examined for its validity and reliability to assess habitual PA of Greek students. Afterwards, a need analysis was carried out in a) a cross sectional sample of 911 students from an urban area (11, 14 and 17 years olds, b) 103 elementary and secondary PE teachers, and c) 17 schools. The students answered the PALQ in order to depict a profile of their lifestyle and PA patterns. The teachers answered a questionnaire in order to evaluate their knowledge, attitudes and self-efficacy towards teaching health related exercise (HRE). A checklist has been used in order to establish the nature and extent of PA promotion in a sample of elementary and secondary schools. The results showed that: a) a large proportion of students adopted a sedentary lifestyle and were inadequately active to obtain health benefits, b) teachers' had limited ability in promoting effectively HR issues, and c) schools provided limited sport programmes and facilities. The overall finding of the need analysis justified the need for intervention and advocated the adoption of an ecological approach to promote PA Based on the Active School initiative (Almond & McGeorge, 1995), a school based intervention programme has been set up in order to a) promote students' participation in physical activity and sport and to enhance their knowledge on health related (HR) issues, b) increase teachers' knowledge and effectiveness on teaching HR exercise. The decisions about the intervention contents and priorities were based on the findings of the need analysis taking into consideration the cost and the resources. The intervention strategy and the implementation process focused on: a) the teachers' training, b) the creation and the provision of the necessary resources (PE curriculum, a handbook and a CD-Rom for the teachers and two books for the students), c) the creation of a positive and enjoyable learning PE environment, and d) the co-operation between school and out of school health and sport alliances. The intervention programme was applied in 9 elementary and 5 secondary schools for a period of six months and involved 15 PE teachers. A quasi-experimental design with a control group was applied (experimental group N1=699 and control group N2=213). A number of different parameters were estimated at the beginning, during and at the end of the program. The intervention process was monitored on a weekly basis by the author and the school teachers. The effectiveness of the intervention was evaluated in terms of: a) students' behaviour, fitness, self-efficacy, intrinsic motivation, intentions, and attitudes related to PA, b) teachers' knowledge, attitudes and self-efficacy on teaching HR issues, and c) the broader impact of the programme on the school ethos. The intervention implementation and effectiveness was also assessed by an external evaluator. The overall purpose of the intervention was to examine the applicability of promoting PA throughout school environment by creating an innovative and realistic framework for school physical education lesson. The findings of this thesis were very encouraging. Significant differences have been observed in most of the evaluated variables both, for students (fitness, attitudes, self-efficacy, PA level), for teachers (knowledge) and schools' ethos. However, this pioneer study revealed a number of key considerations and issues in designing intervention programmes to promote PA throughout schools in urban areas.