If you are talking about “percentage” numbers (95% being an A), most elementary schools I am familiar with do not do this. Many of the assessments teachers use in the elementary grades cannot be boiled down to a percentage. Instead, they use rubrics and other means to determine a grade.
As a parent, I am not a fan of letter grades. While you think you know what an A or a B means, it may mean something different to another person. A grade should reflect what a student knows and is able to do - letter grades often include other things that are not necessarily reflective of learning.
If you have a question about how your child is doing in a particular subject, talk to the teacher. S/he should be able to tell you how your child is meeting the Standards of Learning and how instruction is meeting your child’s needs.

I have a 4th grader in Prince William County school system. He started getting actual letter grades in third grade, rather than the S system. Last, year he got all A's with the occasional B or B+. So, I didn't look that closely at the grading system. So, he got his first report card this school year and he got 3 B's and 2 A's. Still good, but I questioned what the exact number grades were. After many emails back and forth with the teacher, she can't give me an actual number. What happened to getting an average of all work done for the quarter and writing that NUMBER on the report card?? I can read a number and translate that to a letter grade using a grading key. When they give a letter grade where a letter stands for a range of numbers, that is not helpful. For example, a B is anywhere from 80 to 86. So, I don't know if my kid is one point from a C+ or a B+. Do other counties do this backwards grading system? Also, do any teachers or parents out there have a reason why PWC's grading system is so messed up?