Fairly well-off family in the Ozarks, USA. We only say "dinner" when it's a special occasion and it isn't in the morning. For normal meals it's breakfast, lunch, supper. Most of my classmates in elementary school (many of whom had not enjoyed those "changing socioeconomic realities") were the same.
I feel like you're conflating "traditional agrarian" with "rural." I also feel like you're conflating "changing socioeconomic realities" with "people getting rich or well-off."
Was your elementary school in a one-room schoolhouse? Did most people go home for the mid-day meal? Was school in session through the summer and winter with breaks for the planting season and the harvest? Did most people stop going after 6th, 7th, or 8th grade? If not, then I feel like your post may be non-responsive to mine.
Yes I probably misunderstood you, because I have no idea what you meant by "standard American English". I'm an American and I speak English, and my rural neighbors are the same, so I thought I would report my observations. Around here we rarely use the word "dinner" for meals eaten in one's own home.
