how can my son a 5th grader be able to design an expermient with a lab report that theaches others how to use a balance correctly
I would start with what type of balance is he going to use? Is it a modern top pan 'balance'
like these
http://www.labsource.co.uk/shop/index.php?main_page=index&cPath=402_562
or a more traditional balance, either unequal or equal arm type.
He then needs to decide what constitues using the balance correctly, for example, not overloaded, kept clean, kept level, amongst others.
Some of things being taught are generic in that these will be the same for any experiment, such as keeping the balance clean.
Hope this helps