Not a teacher
English is the one language I'm familiar with, which uses object pronouns (like me, him, her, us) in a 'strange' way. E.g. It's me, that's us etc. In the objective case. They are all correct sentences. But in many other languages we say It's I or That's we - in the nominative case, which is incorrect in English. E.g. in German 'Das bin ich', 'Das sind wir' (the same is in Russian). Nominative is the right case in these languages for these sentences. In other circumstances you have to use object pronouns the right way. Cp. 'I gave him my book', 'He is doing my homework' . Both are in the same cases as in other languages. This 'strange' usage of object pronouns leads to the fact, that many people say them wrong, but it's sounds like they are right sentences. I hope you understand, what I mean