Deleting Records From Multiple Tables In SQL Server

I'm new to relational database concepts and designs, but what i've learned so far has been helpful. I now know how to select certain records from multiple tables using joins, etc. Now I need info on how to do complete deletes. I've tried reading articles on cascading deletes, but the people writing them are so verbose that they are confusing to understand for a beginner. I hope someone could help me with this problem.



I have sql server 2005. I use visual studio 2005. In the database I've created the following tables(with their column names):



Table 1: Classes --Columns: ClassID, ClassName

Table 2: Roster--Columns: ClassID, StudentID, Student Name

Table 3: Assignments--Columns: ClassID, AssignmentID, AssignmentName

Table 4: Scores--StudentID, AssignmentID, Score



What I can't seem to figure out is how can I delete a class (ClassID) from Classes and as a result of this one deletion, delete all students in the Roster table associated with that class, delete all assignments associated with that class, delete all scores associated with all assignments associated with that class in one DELETE sql statement.



What I tried to do in sql server management studio is set the ClassID in Classes as a primary key, then set foreign keys to the other three tables. However, also set AssignmentID in Table 4 as a foreign key to Table 3.



The stored procedure I created was



DELETE FROM Classes WHERE ClassID=@classid



I thought, since I established ClassID as a primary key in Classes, that by deleting it, it would also delete all other rows in the foreign tables that have the same value in their ClassID columns. But I get errors when I run the query. The error said:



The DELETE statement conflicted with the REFERENCE constraint "FK_Roster_Classes1". The conflict occurred in database "database", table "dbo.Roster", column 'ClassID'.
The statement has been terminated.



What are reference constraints? What are they talking about? Plus is the query correct? If not, how would I go about solving my problem. Would I have to do joins while deleting?

I thought I was doing a cascade delete. The articles I read kept insisting that cascade deletes are deletes where if you delete a record from a parent table, then the rows in the child table will also be deleted, but I get the error.



Did I approach this right? If not, please show me how, and please, please explain it like I'm a four year old.



Further, is there something else I need to do besides assigning primary keys and foreign keys?