In my point of view and experience as OIC of the office of school principal for four years, the school principal greatly influences the implementation of the school curriculum due to his/her function as instructional leader. He monitors and supervises directly his teacher-subordinates because he has the power to do so. 

Dear Ali, are there subordinated entitled a direct task of monitoring and guiding curriculum implementation activities in your school?

Dear Sir, the Overall school academic head,is the most important person and has all the influence towards the school for the reason listed below:-

• manages all curriculum details to be implemented in the school subjects and the implementation process by the subject heads.
• watches and follows and monitors the performance standards of the children at all level and method
• administration of all level children to successfully gain knowledge by the proper evaluation and examinations
• the overall school health administration of all children and staffs below at all level physiologically and psychologically monitored for the best of good healthy up coming of the children and staffs 
• periodic parent and teachers meeting conducted for all good and odd information shared for the best good healthy education for the children
• there are much more to list but to conclude the detail, the top head has the responsibility to get things done and the subject heads has the responsibility to do their share of function BUT the Overall school academic head, makes everything to work in all correct fashion in the required correct order.

Thanks

Dear Noel, the function of subordinates are more on implementation of the program in their grade level. Further, teachers can give their feedback if they did a "walk through" (an evaluation process to see if the curriculum guide matches with learner's materials, and teacher's guide) across the curriculum. Teachers are given the chance to modify some content of the curriculum to suit the needs of the learners. We called it "localization".

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To have a well-conceived and well-implemented curriculum (meaning that there is a high degree of alignment among the stated curriculum, the taught curriculum, and the assessed curriculum, collaboration and coordination among all three persons and their functions is necessary. 

The principal articulates and supports the vision for student learning and supports it with time and resources. The academic officer provides structure and coordination to the curriculum alignment work across and within all departments. The department chair supports his/her teachers in their curriculum alignment work from the perspective of their discipline. 

Depending on how highly structured and how highly mandated curriculum standards and processes are in the particular nation, school system, or school, each of the three roles could be most important in terms of "curriculum management" defined as curriculum design and curriculum evaluation. As Ali pointed out, curriculum implementation that the students experience is dependent on individual instructors since none of the roles mentioned, separately or together, can monitor a high proportion of curriculum implementation.

School curriculum is one of the organizational components that must keep abreast with changing times. Curriculum does not operate in a vacuum. It is, itself, influenced often in a subtle and indirect manner, by pressures from the society.

the adoption model stresses on the principal to take initiative, in marketing curriculum change in

an institution; The school does not function in isolation and is not a closed system, other structures should therefore be involved.

the Intergrative development model embarks on participatory decision making strategies, thus involving the staff members too. The groups  impacts  the management of curriculum issues, where the personnel with different expertise  assist others in team building.

In the change agent model the principal plays the role of supporter of innovation and give responsibility to curriculum designers as they can influence all essential elements of the curriculum.

So examination of these models suggest that principal is always in the scene.