Mr. Hart is an "old history teacher" of Manny's. When Manny's mother decides to have him transfer to a better school, Manny must make a special trip down to his high school to get a copy of his grades. As he waits for a bus to take him home, Manny runs into Mr. Hart, who asks him why he is there. When Manny tells him, Mr. Hart, who can't seem to stop staring at his old student's ragged footwear, insists that he give Manny a ride home, and pressures him to take $20 to help pay for school supplies.
Manny does not want to take the money, because, among other things, he does not believe that, in the end, he will be able to switch schools. He assures Mr. Hart that he has money, but the teacher is insistent, and slips the money forcefully into his hand. Mr. Hart does not drive Manny directly home, but instead takes a route through a more affluent part of the city, and misinterprets Manny's nervousness for excitement at his surroundings. When the two arrive at Manny's house, Mr. Hart tries to make small talk with Manny's father, but is politely but firmly rebuffed.
I believe that the chapter describing Mr. Hart and his actions is included in the book to show the extent of the divide between the affluent white and poor Latino population in the city. Mr. Hart is well-meaning, but has no understanding of his students and the lives they live. Mr. Hart gives Manny money despite his protestations, not realizing that his generosity may be interpreted as condecension, and he takes Manny all the way to his home, even though Manny has asked him not to. As a result, Manny's father is angry, as Manny had known he would be, and he cynically takes the money Mr. Hart has given his son and uses it to go on a drinking binge. Mr. Hart knows nothing about the reality of the lives of young boys like Manny, and he does not pay attention to the warnings and signs that might enable him to better understand. Still, Manny likes Mr. Hart, conceding that he is at least genuine, and that "whatever else one could say about him, Mr. Hart (is) an okay guy."