What is a good theme for "Thank You, M'am", that isn't vague?
A good theme for “Thank You Ma’am” is to not judge a person until you get to know the person.
You could say this is a cliché, but it is a valuable lesson too. Roger thinks Mrs. Jones is an easy target, but she turns out to be a fighter. When he tries to steal her purse, she knocks him down. Then she surprises him again by taking him home, making him wash his face, and then cooking for him.
Roger is a surprise too. He ends up being honest and respectful. He wants her to trust him. He is misguided, but not really a bad kid.
Mrs. Jones surprises him again by admitting she made some wrong decisions as a younger person.
You thought I was going to say but, didn’t you? You thought I was going to say, but I didn’t snatch people’s pocketbooks. Well, I wasn’t going to say that." Pause. Silence. "I have done things, too, which I would not tell you. (p. 3)
Mrs. Jones has a past too. Roger learns a lot from this encounter, but the main thing he learns is that you should not judge a book by its cover.