At primary school i was the "nice kid" and the teachers forced me to play with the girl that nobody liked. This made my friends not want to play with me, as i felt i couldn't say no to an adult/teacher, so i ended up getting excluded too.
Now the reason nobody wanted to play with her is because she wasn't nice. She almost got her dad arrested by screaming she didn't know him in the middle of a busy street when he had been forced to pick her up as she was refusing to walk as she didn't want to go where they were going. She was very bossy, wanted it 100% her way with no compromise at all and she was violent if she didn't get hr own way. Usually pushing but also some hitting/smacking.
Forcing a child to interact with someone they don't like, are scared/intimidated by or otherwise want to avoid is cruel. sure, th teachers don't want one kid left alone, and i'm sure that kids parents doesn't want their child left out, but if their child is difficult and is alienating themselves by their behaviour the other kids shouldn't effectively be punished or forced to put up with it. An adult wouldn't interact with someone they don't like, so why should a child?
I was also genuinely bullied at primary school too though, by the male i was forced to sit next to (thanks alphabetical seating plan). He would verbally abuse me, but he would also physically hurt me too. He repeatedly stabbed pencils in my arm trying to make me cry, i went to the teacher and told her, she looked at my arm, said the wounds didn't look like stab marks (true they didn't as it was a coloured pencil he used and i had an allergic reaction to the colouring in it) and basically called me a liar and didn't do anything. Another time he slapped me across the face mid lesson, leaving a hand print, and another girl on our table went and told her and she point blank refused to beleive something like that could/did happen in her classroom on her watch and as she didnt see it, insisted it didn't happen. That set me up to not trust teachers to help when i was being bullied, i was made to sit next to him the rest of the year and the year after too, and when i went on to highschool i had no faith in reporting being bullied, even when it go to the point i was suicidal, having panic attacks and became so ill i had to drop out of school.