However.

The entire year, your textbooks, your teacher, your in-class practice, was walking you through the specific commands you need to select to actually do the things, like graphing and solving.

If little Timmy is unable to read the manual about how to do math he doesn't yet know with whatever his specific calculator is, he is at a severe disadvantage, and the teacher basically cannot help him.

A friend in high school bucked the trend and used a casio in our TI based education, and did just fine for himself, but he was apparently a smart kid.