Average of a Count

I am trying to take the average number of students in a class by counting their school_id's but there are multiple classes that are being taught. Any ideas?

This is what i have

SQL> SELECT AVG(COUNT(S.STUDENT_ID)) AS STUDENTS_PER_CLASS
2 FROM STUDENTS S, STUDENT_CLASS U, CLASS C, TEACHER T
3 WHERE S.STUDENT_ID = U.STUDENT_ID AND U.CLASS_ID = C.CLASS_ID
4 AND C.TEACHER_ID = T.TEACHER_ID
5 GROUP BY S.STUDENT_ID;

What is wrong with this?

You really need just one table, if you have difficulties visualizing the results use two queries, the first one (nested) will get the count per class, the second (outer one) will average those counts

Is that not what I am doing my first one (nested)is getting the count for the class and the outer one is averaging right?

No

the course you are taking is not teaching you JOIN syntax