Now, here is s point of sematics.
'Apprentice' is used as a general term for anyone whi is learning from someone else. hence, Maul is known as an Apprentice even though he is bloody hard, easily as powerful as any Knight.
'Padawan' is the actual term used for a Jedi who is out of school but not yet a Knight- a University student on a field trip, if you like. But a Padawan is ALSO an apprentice, as he is learning. So is a Knight taking lessons from a Master.