Confused with volleyball substitutions!

Question
I am desperately trying to figure out how to do the substitutions for my middle school team. I was told that I could only substitute one player for one player throughout the entire set. I'm finding out that is incorrect. I have searched the Internet and many volleyball coaching books to clarify the rules of substitution and I am left confused and frustrated. Can you suggest a resource, or can you explain the rules? I feel like I am being really thick-headed, but I just don't get it. We get 18 subs, and we don't play a libero at our level in Ohio. I would appreciate any advice you could give me. Thank you!

Answer
Good morning Keri:

Let's get right after it.

The #1 question I need you to answer:  What rule book are you using?  That will be the key to me helping you.  You say you get 18 subs....so I'm assuming you're using the National Federation Rule Book.  (Sometimes coaches have no rule book, and/or they really don't' know what rule book the refs are using....that is, if they have real refs at all.  If this is the case, then none of what I have explained below may make any difference.)  

OK, if you're using the NF rule book, then what you've been told about substituting is wrong.

Let's say jerseys #1, #11 and #21 are 3 of your starters.  Sometime during the match you put in #2 in for #1, and then 5 minutes later you put in #3 for #2, then later put in #4 in for #3. All this is 100% legal, and it has been 100% legal since i started coaching vball in 1984.

OK, let's look at where you are sub-wise:  You've now used 3 subs, and the ONLY restrictions you have at this point are:
a) 15 subs remaining, and;
b) #1/#2/#3/#4 can ONLY play in THAT spot.  In other words, you cannot sub 1, 2, 3 or 4 in for #11 or #21.  #1/2/3/4 are all "locked" into that one spot.  But the good news is that you can later sub in 3 for 4, then 1 for 3, then 4 back in for 1, then 2 in for 4, etc.  This is legal.  And it's been 100% legal since 1984, and has never changed (if you're using the NF rule book).  

If this hasn't answered your questions, please let me know.  
The rule isn't that complicated, but YES some refs misunderstand it.  

I hope you have a moment to visit me at www.coachhouser.com!  I think you'll like the smiling faces.   :)  

Coach Houser
Roanoke, Va