I know what you mean. One time my mother said “Don’t let anybody tell you that you are not smart!” I was around 12 years old also. Something about the way she said it made me believe I was going to be hearing that from people. It didn’t sound like a compliment. But, maybe like you, I did something about it. I studied a lot, I guess thinking that knowledge might replace whatever “smartness” I missed out on. She cleared it up when she was old, but, by then, it didn’t matter, of course.