How can I introduce or teach 3rd graders how to use the Correct Verb Form of the verb "to be"?

Question

I want to tell them when to use the words: am, is, are, was, and were....

Answer 1

You may call my thinking archaic, but what is wrong with the good oldfashioned declension of verbs idea?
You know like:

I am
You are
He/she is
we are
you are
they are

I was
You was
He/she was
We were
you were
they were