Bonjour Steven !

Here we used the impersonal "il" (same one as in "il fait beau"), which can also be replaced by "c'est":
"C'est important qu'il apprenne ses leçons."

Note that the "il" version is considered as more elegant.

Have a look at the related lesson: Il est [important] que + subjunctive (Le Subjonctif) = It is [important] for [someone] to ... in French">Il est [important] que + subjunctive (Le Subjonctif) = It is [important] for [someone] to ... in French">Il est [important] que + subjunctive (Le Subjonctif) = It is [important] for [someone] to ... in French">Il est [important] que + subjunctive (Le Subjonctif) = It is [important] for [someone] to ... in French

I hope that's helpful!
À bientôt !