I'll bet you're in the first grade. Second.
4 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.
You can hear this line at 00:24:36 in the Blu-ray version of the movie.
Quote context
[...]
- Would you please tell her that you're not really Santa Claus, that there actually is no such person?
- I'm sorry to disagree with you. Not only is there such a person, but here I am to prove it.
- No, no, no. You misunderstand. I want you to tell her the truth.
- I'll bet you're in the first grade. Second.
- Oh. It's a progressive school.
- May I have this gentleman's employment card, please?
[...]