@ProfessorPlum168 The CA state champ ran just under 1:52 this year and is going to Cal, where they’ll expect him to score at the PAC 12 meet within a few years. He didn’t break 1:54 as a junior. 1-2 second annual improvement is pretty common with young guys in the 800, so a lot of those runners you’re thinking of were probably in the 1:50-1:52 range in HS (roughly top 30 in the nation). Or else they’re converted 400 meter runners, which is pretty common.
You’re right that it’s a big gap from there to 2 flat. But, in addition to what @homerdog mentions about differences between D1 and lac, what’s intriguing about the OP’s son is that he’s undertrained and has decent speed. (A lot of 2 flat CA kids have been running 60 mile weeks for years and can’t break 55 in the 400). Here’s what a D3 coach might see: a kid who ran 53 as a soph might get to 51 as a senior; with that kind of speed and a year of solid aerobic training, that 2 flat could become a 1:56-7 or better as a senior, 1:55 the first year of college. That’s an athlete that can score in the 8 and run the 4x4 in many D3 conferences. None of that is guaranteed, of course, and few coaches will choose that potential over an actual 51/1:56 junior. But I do think the short training history and the decent speed puts the 2 flat in a different perspective.