The tables which have to be used by the students when they solve the tasks are stored in one or more schemas.
The tables are ready for selecting since they were previously populated.
The students execute their solutions (as program codes) on these tables.
The students have only read privilege on these schemas.
If they want to update or delete the contents of the tables in these schemas as a part of the task, they have to make a copy of the required tables in their own schema.