No, having a poor kid in the class does not negatively affect your kid. Having a poor performing kids that requires more resources and attention does.

No, the reason (in my case) was because the public schools prioritize social agendas over academic quality. My kids can do advanced math. My neighbor's kids estimate or guess. I hope the public schools in my area get de-funded. They are a waste of tax payer money. My choice had nothing to do with who is poor or rich.