"It's not hard to earn at least Bs on basic high-school materials; having all Cs shows a lack of ability to do the hard work or a difficulty with or lack of commitment to basic academics."
And it might also show that the kid in question partied through high school, which I suppose is a lack of commitment. But we're talking about teenagers. Some will succeed in academics later on if given a chance.
I was a late bloomer. I partied and had a damn good time in high school, doing the minimum I could to get by. I showed up. That was 80%. After graduating from high school, I worked, played in bands, dated women and continued to party for the rest of that year. My parents then read me the riot act.
Back in the 70s, some of the large land grant universities had less stringent admissions requirements than they do today. I was admitted to one. It was just as difficult to do well there back then as it is now but they'd let you try. And lots of students did flunk out. I knew it was for real. I either had to work or go to school. Having already worked a series of shit jobs for asshole bosses, I was motivated. I made the dean's list for 5 consecutive semesters and was admitted to engineering school, eventually graduating with honors. I've been doing technical work for 33 years.
Today, that would be way more difficult. The admissions requirements are so stringent today, late bloomers would not be admitted. They would have to prove themselves in a community college first and then maybe they would be admitted. They would then have to meet the requirements of the engineering school which is now highly selective. Assuming they were admitted and completed the degree, it would probably have taken about 7 or 8 years to get that degree. Most who enter engineering school today straight from high school take 5 years to finish.
I understand why they tightened the admissions requirements at my alma mater. Too many students were flunking out and it looked bad. The board of governors pressured the university into adopting the same requirements other universities used. The way I see it, the exclusion of late bloomers was a kind of collateral damage.