The morning of the second day of school, Via asks Mom to pick her up after school. Mom insists that Miranda's mom can drive Via as she supposedly did the day before, while Dad insists that Via is old enough to take the subway by herself. Mom is perplexed both at Via's request and Dad's answer, so she asks if something is going on. Via spitefully reminds Mom that she never came back to check on her last night like she said she would, and Mom is distraught when she realizes her mistake. Her apology makes Via feel bad for making Mom feel bad.
Via's guilt trip is an unkind thing to do, though Mom's reaction makes it clear that she's spread thin trying to care for her children. Dad appears to recognize that Via is more independent than Mom wants to think, though this is likely at the root of the problem Mom and Via are having: Mom simultaneously forces Via to be independent while not actually believing that Via is old enough to be that independent.
Mom asks if there's something going on with Miranda, and Via explains that Miranda is acting like a jerk. August pipes up that Miranda isn't a jerk, but Mom quickly tries to defuse the brewing argument by agreeing to pick Via up from school. Dad impatiently says that if Via is old enough to read War and Peace, she's old enough to take the subway alone. He rushes Via out the door, and Via waves at Mom when Mom yells for her to call before she gets on the subway. Dad turns around, smiles, and yells "War and Peace!" at Mom.
War and Peace is a difficult novel that's more than a thousand pages long. Though it's clearly a major undertaking, it's important to recognize that simply being able to get through such a novel doesn't mean that someone is fully mature or able to handle potentially dangerous situations like taking the subway alone.