I think more people will stop to read the condtions if you let them know as the very first thing that you're looking to suppliment a school library.  Then let them know what you're looking for. Then even if they never fill other RC's they might read on if it's for a good cause.

I'm not very good with wording RC's, so hopefully someone else will be able to help you word it nicely.

I agree that school library should go first. 

Be sure that your RC is not too dense.  Spacing is very important on long RCs.  Use bullets or some such thing to break up the large square of text.

Be polite.  Don't use demand terms like "must" and "should".  Make it clear but not demanding.  (And oh boy, is that ever hard!)

Here is an old thread that helped me when I edited my RC.  How to write a RC

And put your rough draft RC here so we can comment and help edit.

Here's a go at it:

Since this book is being requested for a <elementary? middle? high?>school library, please ensure:

• if it is a harcover, it should either have illustrations on the front cover OR include the dust jacket .
• if it is listed as "unknown binding," only send the book if it is a hardcover which meets the above condition.
• in YOUR subjective judgment, it can last a few readings in a school library.

Thank you for your help and attention to these Requestor Conditions.

With this RC, you might get some books which don't meet your (=Andrea's) defition of "sturdy enough for a school library" but I think taking this chance is better than asking for an evaluation of "good to like new" The reader feels assured that  the requestor knows  a subjecctive opinion is being asked of her. This phrasing implies that you are not going to RWAP if it is within postability guidelines (but hopefully you managed to weed out the barely postables)

Do you have any conditions for paperback books? Or do you just don't request them? I ask because this might still confuse a sender if you request a paperback book.

Feel free to edit further.

Andrea,

I know that you are also concerned about age, but limiting the age can also hinder.  I have ordered some books for my grandkids that are older (one is 1979 and other is 1983) and are in excellent shape (these are hardback, Disney stories).  They are a little worn on the edges but otherwise in very good shape.  I think they could handle a couple of years with second and third graders. 

So I would suggest a certain age span, but also leave the age of the books up to the sender; they should be able to determine if the books can survive kids for a couple of years.  Especially those who have kids or grandkids and know what the books will go through.

I can remember buying books when my kids were little and they took very good care of them.  Even at 20 years of age they looked almost brand new.  Now, my grandkids, they can be  hard on books; I asked my daughter about books and she told me that after two or three years several had to be tossed due to how her kids treated them.   

Shameful to me.  I know I taught her better, but . . .

Janette