Final answer:
The protection of a teacher's free expression depends on whether it substantially interferes with school discipline or others' rights, as determined by pivotal cases like Tinker v. Des Moines and Hazelwood v. Kuhlmeier.
Step-by-step explanation:
When assessing whether a teacher's right to free expression is protected, it is important to consider if the behavior in question is disruptive to the learning environment or not. Critical Supreme Court cases such as Tinker v. Des Moines (1969) and Hazelwood v. Kuhlmeier (1988) have set precedents that the First Amendment rights of individuals in a school setting can be limited if their expression creates substantial interference with school discipline or infringes on the rights of others. In Tinker v. Des Moines, the Supreme Court ruled that students do not lose their First Amendment rights when they step onto school property, but the expression must not materially and substantially interfere with school operations. The Bethel School District v. Fraser (1986) case further emphasized that schools can regulate speech that is lewd and indecent, even if not obscene, under the guise of protecting minors and upholding school discipline.