The study aimed to assess the effectiveness of a training program based on the Interconnected Model of Professional Growth (IMPG) on the self-efficacy beliefs towards teaching and teaching performance of science teachers who teach grade eight as well as its impact on the academic achievement of their students in the Sultanate of Oman. The study used the Quasi-experimental research method (pre- and post-design for two groups: experimental and control) with a mixed explanatory sequential design. To obtain a greater depth in the interpretation of the quantitative data results on the training program's effectiveness, focused interviews with eight teachers from the experimental group (n = 8) were used. The teachers of the experimental group (n = 15) were subjected to the training program based on the IMPG, while the control group (n = 15) was in the normal course of planning and implementing lessons individually within the subjects of the second semester of the academic year 2020/2021. The students of the experimental teacher's group were (925), while the students of the control group teachers were (850). To assess the effectiveness of the program, three research instruments were administered. The first one was the Science Teaching Efficacy Belief Scale (STEBI-B) by Enochs & Riggs (1990), which includes two dimensions: The Personal Science Teaching Efficacy Belief and the Teaching Outcome Expectancy. Its psychometric parameters were verified through content validity and reliability, whose value for the whole scale was (0.73). The second instrument was the classroom observation card for the teaching performance of science teachers. The card consisted of (32) skills after presenting it to a group of judges to verify its validity. The skills were distributed over eight elements of the classroom situation. Using the method of Inter-rater- reliability agreement of the observers, the percentage of agreement reached (88.75%). The third tool was the academic achievement test. Its psychometric parameters were verified through content validity, test item analysis, and the calculation of its reliability coefficient through the test-retest method. The value of the Pearson correlation coefficient between the two applications of the test was (0.82), and the average Cronbach alpha coefficient for the two applications was (0.76). Regarding the beliefs of self-efficacy towards teaching, the study concluded that there was no statistically significant difference between the average score of the study sample, while there was a statistically significant difference in favor of the experimental group in the average score in the observation card of teaching performance, with an effect size of ( 2 = 0.696). In addition, there were statistically significant differences between the students of the experimental group and the students of the control group in the achievement test in favor of the experimental group students, with an effect size of ( 2 = 0.013).The study recommended taking into account the areas of the IMPG when designing training programs for teachers and adopting the lesson course as a strategy for professional growth at the school level as a training unit.