You will be seeing a lot of grades in the coming weeks. I am often asked what the grades that I give players mean. The big secret here (well it isn't a secret really if you've read my stuff) is that I don't like giving players grades. Grades are, at best, shorthand. Nevertheless, everybody wants grades, so here is how I define them.
Grade A prospects are the elite. They have a good chance of becoming stars or superstars. Grade A prospects should develop into major league regulars, if injuries or other problems don't intervene. Note that is a major "if" in some cases.
Grade B prospects have a good chance to enjoy successful careers. Some will develop into stars, some will not. Most end up spending several years in the majors, at the very least in a marginal role.
Grade C prospects are the most common type. These are guys who have something positive going for them, but who have a significant question mark or three, or who are just too far away from the majors to get an accurate feel for. A few Grade C guys, especially at the lower levels, do develop into stars. Many end up as role players or bench guys. Some don't make it at all.
Also note that there is diversity within each category and there are many borderline cases. A player rated as a Grade B+ may every well become a star, but there may be something that gives some doubt at this stage of his career, for example a player with great tools but who lacks refinement, experience, or who we just don't have a lot of data for. A Grade C+ is actually good praise coming from me, and some C+ prospects turn out very well indeed.
Again, keep in mind that all grades are shorthand. You have to read the full comment for my full opinion about a player, the letter grade only tells you so much. A Grade C prospect in rookie ball could end up being very impressive, while a Grade C prospect in Triple-A is likely just a future role player.
Here are some examples of grade progressions over the last few years.
Mike Trout: 2010: Grade B+; 2011: Grade A, 2012: Grade A
Bryce Harper: 2011: Grade A; 2012: Grade A
Matt Harvey: 2011: Grade B; 2012: Grade B+
Pete Kozma: 2008: Grade B-; 2009: Grade C+; 2010: Grade C; 2011: Grade C, 2012: Grade C
Will Middlebrooks: 2008: Grade B-; 2009: Grade C; 2010: Grade C; 2011: Grade C+; 2012: Grade B
Wade Miley: 2009: Grade B-; 2010: Grade C+; 2011: Grade B-; 2012: Grade C+
Jurickson Profar: 2011: Grade B+; 2012: Grade A
Manny Machado: 2012: Grade A
Mike Moustakas: 2008: Grade B+; 2009: Grade A-; 2010: Grade B; 2011: Grade A