Which of the following is NOT allowed in terms of relationships with students?

The option regarding sexual relations is correct because educational institutions have strict policies that prohibit any sexual relationships between teachers or substitute teachers and students. Such relationships can create significant ethical concerns, undermine the trust that is essential in the teacher-student dynamic, and pose serious legal implications.

Mentorship, friendship, and academic support are generally permitted under appropriate boundaries and context. Mentorship provides guidance and support for students' academic and personal growth, while friendships, as long as they are appropriate and professional, can foster a positive classroom environment. Academic support is part of a teacher's role in helping students succeed in their studies. However, all these positive relationships must be maintained within professional boundaries to ensure a safe and conducive learning environment. Thus, sexual relations represent a clear violation of ethical standards within educational settings.