This research study was carried out to develop a model for in-service training of secondary school science teachers. Objectives of the study were to assess the present system of in-service training of secondary school science teachers; develop a model for the in-service training of secondary school science teachers; and make recommendations for the improvement of in-service training of secondary school science teachers. In order to achieve the objectives of the study, three questionnaires were developed for trainees (secondary school science teachers), master trainers and head teachers. All the questionnaires were comprised of a 4-point scale and one open-ended question. The questionnaires developed for trainees, master trainers, and head teachers were comprised of 38, 25 and 24 items respectively. The population of the study were 2191 trainee teachers, 76 master trainers, and 1509 head teachers. The questionnaires were administered to 724 trainee teachers, 28 master trainers, and 432 head teachers of 432 institutions (schools). The response rate of trainees was 78.72%, master trainers 100% and head teachers 82.63%. The study was conducted in four randomly-selected districts of Southern Punjab. The data collected through questionnaires were tabulated, analysed, and interpreted. Study findings suggest that a majority of trainee teachers, master trainers, and head teachers believed that training courses were a source of greater awareness regarding content, teaching methods, and the use of A.V. aids. The trainees and master trainers considered that the lecture and activity methods were used during the training, contents of textbooks were taught, got perfection over the contents, understood basic principles of teaching and A.V. aids were used during the training of science subjects. Most of the head teachers stated that the majority of teachers’ performance improved, changes in teachers'' behaviour occurred, and evaluation became a prominent skill due to attending training courses. It was concluded that lacking use of practical work, lack of expertise in using laboratory equipments, low TA/DA (Travelling Allowance/ Daily Allowance), and communication gaps were the major drawbacks of training programmes. In light of conclusions, it was recommended that withdrawal of teachers from schools for INSET should be minimized, training centres should be established at local or tehsil levels, lecture method should be used to the least extent, modern methods of teaching (e.g. demonstration and activity methods) should be used and the nomination of teachers should be made on merit. Pre-test and post-test may be designed and administered on a compulsory basis to determine the academic and pedagogical status of participants. There should be continuous feedback, monitoring, and evaluation for INSET programmes. On the basis of recommendations, a proposed model for the in-service training for secondary school science teachers was developed.