Mom accuses her 11-year-old son's 5th grade teacher of being unprofessional for writing him a letter congratulating him on improving his class participation: 'She wrote something like, I am really proud of how brave you have been lately.'

No good deed goes unpunished, and teachers are punished twice as hard. 

Working with kids means you have to watch what you say far more than most other professionals. If you tell your coworker something off-color about your personal life, there's a good chance that they will think, "Wow, that was kind of weird," forget about it, and never bring it up ever again. If you say the wrong thing to a kid, there's a good chance they'll tell their parents, who will tell the school, and you'll get in deep trouble. It's not that HR offices don't punish office workers for saying unprofessional things. It's just that HR offices don't care whether their employees' moms like what their coworkers say, so they don't put much effort into pleasing them. Schools care a lot about keeping parents happy because if they move out of the district, the district will have less money. 

Teachers shouldn't just watch what they say around kids because saying the wrong thing might get them in trouble. It's essential to have healthy teacher-student relationships that don't cross any inappropriate boundaries. These boundaries can get fuzzy when a teacher has a close relationship with a student. Would it be improper for a teacher to attend a favorite student's first communion if they can't attend all of their students' first communions, because attending only one would be unfair?  Is it wrong to have dinner with your favorite student and their parents after the school year has ended to develop a friendship outside the classroom? There is no clear answer.