This is abnormal correct?

For a good student to suddenly drop their grades, I would suspect that either something was going on with that child’s learning, or the child wasn’t working up to their potential. If this was “long ago” as you state, your parents may not have known you struggled with a learning disability. (If you do—it doesn’t say in your OP, but you seem to infer it?)

Our house rule was that you had to try your best in school. If they came home with a poor grade and I knew they had zeros from assignments they didn’t turn in (we could see the online grade book), they did get grounded from screen time during the school week. They also had to do their homework with me at the table.

Are you saying that being grounded for getting some lower grades doesn't seem fair because it could be due to the work being more difficult rather than because the child wasn't working hard enough?

I don't think that was abnormal. I know kids now who are punished for getting bad grades. For my DD, I do expect high grades, because I know she is capable. She wouldn't get in trouble for a C, if she had been working hard though. If she was blowing off the class, we'd have a nice long talk and probably involve a tutor.

I was regularly grounded or punished for bringing home Cs. School came easy to me, so all As and Bs were attainable and my parents knew that - truthfully, I probably could've had straight As if I had *really* applied myself. When I was making Cs, it was because I was being lazy or slacking off. ETA: I graduated in 96 so this was 80s/90s

I only wish my mom grounded us for C's.  believe me, that would have been a dream punishment compared to what we got. 

I think it's just different.
I had a kid that we celebrated C's and another we punished for C's. The first one worked hard for them, the second was capable of more.

I think that years ago, that was a pretty typical parenting response. It's not necessarily the approach I use today- but as we know better, we do better.

My personal policy as a parent is that if you are doing your best (turning in homework, studying, asking the teacher for help, taking advantage of tutoring and/or study groups) then I'll be just as proud of an F as I am of an A - even prouder in fact, if that A came easy and that F involved hard work.

My kids are/were generally A/B students but not always. Sometimes their grades dropped because they couldn't be bothered to turn in homework, sometimes because they were in a class that was very very hard for them. If you're not turning in homework, then we instituted mandatory, parent-supervised homework/study time (and that tended to cut into screen time, lol). If you're struggling in a class, we encouraged talking to the teacher, going to before/after school tutoring if available, joining study groups with classmates (as available) etc...

DS took AP Calculus his senior year - he struggled SO much with it. He had a great teacher, he paid attention in class, he attempted all the homework, he met with the teacher before school for tutoring, he met with classmates every weekend to study together...he got a 15 on the first test - even the teacher was shocked at his low test scores. Let me tell you how excited we all were when he had pulled his grade up to a 50 by the end of 1st term. It kept going up slowly from there and he passed in the end with a low C. He didn't pass the AP test - and that was okay. He had done his best and we were proud of him.

My youngest has never once passed a spelling test - not once. Thankfully she's past the spelling test grades now but we strongly suspect that there's some sort of learning challenge involved there (the school doesn't disagree but her grades don't justify further testing to them - she's already on a dual IEP for communication and gifted). There's no point of punishing her for poor spelling grades (and if they negatively impacted her Language Arts grade, no point on that either) - I know she's studying, she studied harder for spelling than for everything else combined. We focus on work-arounds at this point (spell-check, dictionary, asking someone how to spell a word, asking someone to check written work for spelling errors).

I'm not 100% I understand the question but...if it is about being grounded for getting below a "B" - yes, it was common when I was growing up. It was because if we got mostly As and Bs, and then a C popped in there, our parents would think we were spending too much time doing other things instead of focusing on our studies (which 99% of the time was true) - being grounded did help raise our grades back up because we spent more time studying/doing homework than watching TV. My parents were super strict when they grounded us, they could tell when we needed to focus more time on our studies.

So, depending on when/where you grew up, I'd say it was common to be grounded when you brought home poor grades.

I remember being grounded from tv in elementary school in fifth grade. My mother took away my beloved Charlie's Angels. I probably wasn't doing my best though, but to be fair, my elementary school had a much harder ranking scale for percents than my kids did. Now a B would have been a C.

Wow! You did well in grades 1 - 4 and then was grounded from 5th grade on for C's. That is being grounded for 8 years. Your parents definitely did not check into your grades to see what happened. I hope you raised your own kids differently.

I'm always surprised at the number of people that expect above average and exceptional grades from their kids. Far more than 50% of the population, which makes me wonder how grades are assigned. 

As a teacher it seems to me that parents/students/everyone? expects that if basic requirements state students should be able to do ABC, and a child does ABC, then the child should get an A. Completing the minimum requirement means you got an A. Even if the average student is able to do ABC. In my class, students should be able to do ABCDE in order to get an A. They must be well above average. 

Being a C student is something to be ashamed of, apparently. No one is allowed to be average any more. 

In my own home, we punished our children if their grades dropped because they didn't do their part. If they forgot to turn something in, if they didn't study for a test, etc. If I knew they were struggling with a chapter and the resulting test grade proved it, they were okay in my book. They tried.