Not necessarily. In Jr and Sr high parents would probably have to sign a consent form for their kids fo have blood taken if they don’t know their blood type/parent’s type. So a good hunk of parents would probably say no.
Also, a fantasy situation such as “Bobby’s Mom as A blood and Bobby’s Dad as B blood, what is Bobby?” is different from a real life example. Because a fantasy situation there’s one clear answer for everyone. In a situation like this, not everyone will have the same answer.
They also never learned that punnet square (normally taught in biology or genetics, so if they majored in arts or economics, they wouldn't have taken biology), and some people think that it is randomly decided what your child's blood-type is.
Also, a fantasy situation such as “Bobby’s Mom as A blood and Bobby’s Dad as B blood, what is Bobby?” is different from a real life example. Because a fantasy situation there’s one clear answer for everyone. In a situation like this, not everyone will have the same answer.