By giving time DURING the school day to get the job done, and minimizing red tape. One major problem is that the larger and more heterogenous classes get, the more grading and planning work piles up, and the harder it is to help individuals during class with one-on-one attention. So the teacher ends up using their grading, planning, and lunch time to meet with those students later, and takes all that paperwork home. Administration piles even more kids into the class, saying, "You're not overworked: it was your CHOICE to teach through your break," because they know full well that anyone who chose this profession is going to have a hard time drawing that line when they know there are struggling kids who need the help.

Came here just to make sure this one was mentioned.

There is absolutely no substitute for a live, in-person voice teacher to guide your practice. Shop around—take a first lesson with a few options and try to evaluate who's got the best technique and pedagogy. Also, this is a great goal and very achievable—go for it!