zingally I was like that at school, bone idle. You only need to read my report cards to see that. "Very capable but tends to be lazy", "If Jinty spent as much time on her work as she does staring into space she could do very well", "Needs to show more effort", etc, etc, etc. I didn't really do particularly well at school because, well, bone idle people don't, do they?
Ds1 was exactly the same. Bright, clever, reading and writing before he went to school but as soon as he was faced with one teacher and a class of 30 children he too became bone idle. Work was sent home for him to finish. He was kept in at playtime to do it but he just couldn't seem to get it. All he had to do was keep concentrating and get it done in class time. I suggested there might be problem. The teacher suggested it was "lack of discipline at home", my dMum suggested he was just lazy like me. After all she had all my report cards to show it and his, pretty much matched, mine.
zingally my teacher used to make me stand on my chair or sometimes he would smack my hand with a ruler if I didn't get it done. Ds's teacher liked to tell the rest of the class how slow he was and get them to try to chivvy him along. (A bit like your technique) Two years on and facing the same teacher again for another year and with his self esteem in his boots I asked for him to be assessed and he was diagnosed with ADHD. Lightbulb moment! I have ADD as does ds3 and I will never let ds3 suffer as ds1 and I did. Knowledge is power.
OP do you have any other concerns. Another poster has mentioned dyspraxia and there are other related issues. Go and speak to his teacher. Find out what they are going to do to properly support him and pray he doesn't get zingally next year.
Sorry about the rant but I feel very strongly about this and feel so sad that children are treated in this way. They only have one childhood.