The MLB Scouting scale is a 2-8 scale. Of course, those grades are seldom published anywhere.
It is a good system and we actually use it internally. A 5 grade means MLB average in that tool. So a 5 on the MLB scale would be more like a 9 on the PG scale. In other words, MLB average is excellent for a high school age player.
Once again, there is nothing misleading about the grades. The grade is simply an opinion, just like some MLB Scouts would grade a player a 5, other MLB scouts might grade the same player a 4. Happens all the time, but people just never know it.
Our grades are based on potential, our opinion of a player's ceiling or potential. We use numbers and our eyes to form an opinion. The more we see a player, the more accurate we become. But there is no scientific formula that will tell you with certainty what the 16 year old will be like when he is 21 years old. It's really fairly simple, do you want that opinion or not? I will say that we seem to be consistent with how college recruiters and pro scouts think.
Take a program like Vanderbilt or Florida or most any SEC college. Go to there website and click on their roster. Then you can easily check those players old PG profile and see where they ranked or what their grade was, if they had a grade. Seeing that I haven't done that, I'm just guessing. But I bet you will see that most of those grades will be very high and there will also be some not so high.
The player or parent that thinks a high grade is all it takes would be mistaken. Same goes for those that think a low grade means they are limited. And I see nothing wrong with a young player that believes he is better than what others think. That is not false hope, that is real hope! What is worse, perceived false hope or understanding there is no hope. Some parents will learn, many already know, there are kids out there right now that are the very worst player on their 12-13 year old team and they will become the very best prospect at their high school in 4 or 5 years.