Fridge Brilliance: The movie has been pushing the idea that being educated will get you ahead in life but in the finale, Arthur pulls a sword out of a stone which has nothing to do with education. However, Merlin can see the future. It's possible that he knew Arthur was headed toward some big life-changing event. He didn't know what it was but he knew it was something and wanted him to be ready for it. All that education will make Arthur a better king.
Fridge Horror: Congratulations, Arthur! You're a child king in Medieval England! You're basically surrounded by hostile nations, the country's been in a leaderless quagmire of indecision for most of your lifetime, your trusted advisor flies into a rage and ditches you at the very idea of you being involved in combat, and your only preparation for all this has been the dubious lessons of being turned into amusing animals. ...Good luck! (Thankfully, you're a Disney monarch, so you basically just get a vague, implied Happily Ever After. At least until they decide to make Sword In The Stone 2 but on the bright side you might hook up with a human version of that girl squirrel!
Make note: he's a Disney Character. the instant he has a child he or his wife are ticking time bombs as to who'll die first. it's weird but Disney does not seem to like 2 parent house holds. (until the 2000's)