Yes, I have become THAT mom

Okay, so report cards came home today and I really hate that I have become THAT mom. You know the one who gets a little too caught up in their child's grades. The one who has to restrain herself from calling to speak with the teacher, because there seems to be a problem. Yes, that totally annoying mom is now me. But let me explain...
While I was teaching I was made a project manager on our districts "new" report card adoption. It was my job to oversee the implementation and transition. I liked the new reporting system because it was very specific. Instead of "math" grades the kids were assessed in different areas so you could actually see what the kids could do. Well, parents hated it, because they didn't care about what skills the kid had, they just wanted the A,B,C's. The loudest critics were parents of "A" students who were now not "A" students. Bottom line, it was a total bloodbath, I had to resign and they brought in a mediator to try and find some middle ground. It was a mess, but it did bring up some good questions like "what are the kids really being assessed on" "how important is daily work compared to assessments" "should effort be figured into a grade" "how much of a student's grade is really subjective", etc. The whole grade discussion is very interesting, but I found it is right up there with religion and politics, folks have STRONG opinions and it is best to know your audience before you start the discussion.
So anyway, this December Ben brought home his first report card with letter grades. Kind of a big deal (we are not grade Nazis, but we want him to do well, since he is a bright kid) I must say I was surprised to see a lot of "B-'s". All the papers he was bringing home were always done correctly, he might miss one problem now and then. I chalked it up to the beginning of the year and there was probably other assessments that I was not aware of. So this trimester, we really focused on school work. Spelling tests were something that I know Ben had made no effort on in the first trimester, so that was an easy fix. Ben got A's on all of his tests with the exception of 1 and he got a B. On the report card, he still had a B- in spelling. What up??? The same thing with Math. All of his work coming home showed he got everything right, so why the B?
Okay, before anyone freaks out about B's being good grades and I should lay off, here is my frustration. I just want to know on what are the grades based. If there are other assessments being done, that's fine, just let me know. It just seems a little defeating when you work hard towards something and then there is no payout. Yes, I have unresolved grade issues from my youth and I'm sure Ben could care less, but this really drives me nuts!!!
So now, I have to go into our conference tomorrow and ask the teacher (who I adore and think is a great teacher) to explain her grading system (a question I hated as a teacher). I'm hoping it won't come across as "I don't think you know what you are doing" because I really think she does, it just doesn't seem to match what is coming home and that is my concern. If Ben needs more help, okay, we can help him, but when we see perfect papers coming home how are we to know he needs more?
Ben is bright (he gets that from Joji) and he totally gets the school thing. I have no doubt he will do well. I just like to know all the facts. I've also seen too many teachers give arbitrary grades because they liked or didn't like a kid (can you believe teachers admitted this to me during my report card project, scary) I just want a true picture of when Ben is, that's all.