I am a high school teacher so I thought an outsider perspective would be interesting.
Frankly I spend my entire day with students, I didn't need to read exact transcripts of what their conversations were. I found the chapters incredibly repetitive. Baker was very judgmental towards the lessons he was doing as a sub. He constantly underestimates children's abilities by saying lessons are being taught too young.
There was no conclusion or summation. This would have been more interesting if he spent less time recapping the minutiae of children's conversations and more time reflecting on things.
Also, does he have a perfect memory or was he recording his days with the children to get such exact recall? If he was recording did he have parental permission to record the children? I doubt it.