There’s a good chance when you were younger, you heard classical music in the classroom to try and make you smarter. However, this is a myth - there is no such link between music and intelligence (or that we can measure intelligence for another matter!)
I’ve never heard anyone claim classical music makes you smarter. I have heard people say it makes you focus better, which is true to some extent. This was one of the first things my therapist recommended I try after being diagnosed with adhd. I can’t imagine it isn’t applicable to people without adhd, although probably to varying degrees depending on the person.
The only thing I take issue with is the specification of classical music. Some people have told me this is because classical music doesn’t have words in it, which would distract you instead of help you focus. Not only can classical music have lyrics, but every other genre of music is perfectly capable of not having lyrics. I’m not sure if its even true that the lyrics would distract you in the first place.
Its pretty clear to me that the only reason people play classical music specifically for this purpose is because it makes them feel smart. You could argue that feeling smart might actually help you get things done, but I dislike the perception of classical music as smart people music in general. It’s just a style of music, like every other. There’s nothing that makes it superior or more sophisticated, its just what Europeans liked a few centuries ago.