I think the point behind the essay is to give the college a reason to say yes. I think, particularly for weaker students, that it needs to show that they’re more than so so scores.
Adcoms will see the academic turnaround. And they’ll see that, as happens so often, this is probably a kid who grew up a few months or years behind schedule-- who started freshman year without the same level of maturity as his classmates, but who has now found his groove and is doing better.
I wouldn’t spend an essay explaining that. Instead, I would focus on some of the things those grades don’t show-- a passion for a sport or activity, a desire to help make the world a better place, anything that shows a part of the applicant that has nothing to do with grades.
The Common App has a place for “is there anything else you want us to know?” kind of information-- that’s where he can explain his turnaround. And his guidance counselor can explain a bit in the letter she’ll be writing.
But I would spend that very valuable essay real estate-- those mere 650 words-- on things that the grades don’t show. On the reasons his parents and best buddies and girlfriend think the world of him.