Translation:Every student needs to attend science class.
You are correct and the distinction is not nit-picky. "Taking a class" only means you are registered for it or on the official roster. "Attending a class" means you are physically present at a specific time and place.
When people "take online courses" they are usually free to do coursework at any time and any location. You won't hear people say, "I'm attending an online course this semester." However, it is possible to "attend" a live online chatroom discussion from 5-6 pm on Wednesday.