I think a large part of getting an apprentice to level and pass apprenticeship is having them have a goal.
I've always told my students that level 20 isn't the peak nor the end of the game, it is actually just the beginning. They should concentrate on leveling and gathering sp and leave all the extras aside for when you have the time to devote yourself to them.
Anyone can make it to level 20 in 10 days, if you play an hour a day, straight grinding, no distractions, you can make it to 20.
Part of what I see is the difficulty is that apprentices get caught up with the pets and killing people they don't like at 16 (I've had several get stuck at 16 and red named for a while) rather than using their 10 days wisely.
We will Rise again! - - Ex GS / Retired.