You could paste the following into the SQL view of the query window:
SELECT Max(Student.Marks) AS Expr1
FROM Student
WHERE (((Student.Marks) Not In (select Max(Student.Marks) from Student)));
To do it using the query grid, add the Student table,
Enter "Expr1: Max(Student.Marks)" (but no quotes) into the Field row of the
first column
Enter "Marks" into the Field row and "Student" into the table row, and "Not
In (select max(Student.Marks) from Student)" into the Criteria row of the
second column (no quotes around these, either)
Run the query