Your common sense is failing you because the reasoning isn't sound. Teachers are not super-intelligent all-knowledgeable people. Parents can have the time (stay at home dad homeschooling). Home schooling is 100% 1-on-1 whereas school schooling is at a huge disadvantage to start with 1 teacher per 30+ students. Parents home schooling responsibly have access to the same text books that teachers do. Parents can learn a little bit of how to teach. Parents are more motivated to teach well than a random teacher. Etc.