What grade would a person born in late 2000 be in this upcoming school year?

Going into 9th.

OK: A person can't start kindergarten at 4 in August or September 2005 (late 2005 birthday)

So starts kindergarten at 5 in 2006 - school year 06/07

1st = 2007; 2nd = 2008; 3rd = 2009; 4th = 2010; 5th = 2011;

6th = 2012. 7th = 2013; 8th = 2014,

then starts 9th grade in 2015 !

10

How late in the year? If they were born before September, they should be going into 10th grade, but if they were born between September and December they should be going into 9th.

Unless they got set back or skipped a grade either the 9 or 10th depending exactly how late in the year

It would depend on where that person lived and the laws about exact age of school entry in that place. The person would most likely be going into either ninth or tenth grade.

8th grade