I don't understand why some parents are so obnoxiously over-excited about their child graduating. QUOTE]
because they might be the first in the family to do so. A major accomplishment.
You'll get exclamations of wonderment but that's very true, even in 2016. And it cuts across racial lines (not so much socio-economic). You really see it with boys, not so much with girls.
I had a kid who made it all the way to 11th grade a few years ago. Her family really gave her #### about it since 9th grade had been Senior year for the rest of them. Anyway, she got knocked up after Prom her Junior year. The family was positive she'd drop out then. She didn't and graduated on time. Then she started at PGCC for Nursing That's when the parents kicked her and her kid out of the house. She was "thinking she was better than them". She wasn't she just didn't follow the family's pattern.
She was White, by the way.