The word that names a necessary part of the underlined word "School" is "Student".

Explanation:
To understand why "Student" is the necessary part of the word "School", let's break down the meaning and components of the word "School".

Definition of School:
A school is an institution where students go to receive education or instruction.

Components of School:
1. Students: Students are the primary members of a school. They are the individuals who attend the school to learn and receive education. Without students, a school would not exist or serve its purpose.

2. Teachers: Teachers are the individuals responsible for imparting knowledge and educating the students. They play a vital role in the learning process within a school.

3. Curriculum: The curriculum refers to the set of courses or subjects that students study in a school. It outlines the specific topics and learning objectives that students need to achieve.

4. Classrooms: Classrooms are physical spaces within a school where teaching and learning activities take place. They provide a structured environment for students to engage in educational activities.

5. Facilities: Schools also provide various facilities such as libraries, laboratories, sports facilities, and other resources that support the learning process.

Significance of Students:
Among these components, students are the most essential and necessary part of a school. Without students, a school would lose its purpose and function. Students are the reason why schools exist, as the main objective of a school is to educate and nurture them.

Students bring life and energy to a school. They actively participate in classroom activities, engage in discussions, ask questions, and collaborate with their peers. Their presence and involvement create a vibrant and dynamic learning environment.

Furthermore, students are the ones who benefit from the resources, facilities, and teaching provided by the school. They are the recipients of knowledge, skills, and guidance that will help shape their future.

In conclusion, the word "Student" is a necessary part of the word "School" because students are the primary members and the main reason for the existence of schools. They are the ones who receive education and benefit from the various components and resources that a school provides.