A sharing set is the optimal and standard feature designed specifically for granting high-volume community users access to records associated with their account or contact. For users with a Customer Community license, a sharing set can be configured to grant access to Case records where the Case.AccountId matches the User.Contact.AccountId. This is a declarative, scalable, and purpose-built solution that directly fulfills the requirement without the need for custom code or complex rule administration, making it the most efficient and maintainable option.

A. Use Apex sharing to share cases with the students.

Apex sharing is a programmatic solution for complex scenarios. It is not optimal when a standard declarative feature like a sharing set directly addresses the requirement.

B. Create a sharing rule to share cases with the students.

Sharing rules grant access to roles, territories, or public groups. Customer Community users do not have roles, and this mechanism cannot dynamically grant access based on the user's specific account.

1. Salesforce Help, "Set Up a Sharing Set": This document explicitly states, "Sharing sets grant site users access to records that are associated with their accounts or contacts." It details the process of creating an access mapping, such as User.Contact.AccountId = Case.AccountId, which is the exact solution needed for the scenario.

2. Salesforce Architects, "A Guide to Sharing Architecture" (PDF): In the section "Sharing with External Users" (page 31), this guide describes sharing sets as the primary mechanism for sharing records with high-volume community users. It states, "Sharing sets are the preferred way to share records with external users who have Customer Community, Customer Community Plus, and Partner Community licenses."

3. Salesforce Help, "Experience Cloud User Licenses": This documentation clarifies the capabilities of different community licenses. For the Customer Community license, it notes that these users do not have roles in the Salesforce role hierarchy, which invalidates the use of role-based sharing rules for this license type.