My observation from doing hundreds of interviews at career fairs was the fancy schools (Stanford) had students that were way better at basic questions. This isn’t a perfect metric, but it’s signal.

If your peers in undergrad were your friends, you were probably selecting a non-representative group (smart people you liked) and your job as a TA shows you a more random sample (or even skewed negative, poor students grubbing for grades).

At least that’s my guess (selection bias).

Of course if I’m wrong there’s an even bigger opportunity in undervalued students, but I’ve done enough interviews to believe that’s not true.