Theory:

Did they ever, never spell right
Did they ever make mistakes?
Were they punished in the corner
If they pinched the chocolate flakes?
Explanation:
  
The child then asks questions which are relatable to his own school life. Every child makes mistakes in school and gets punished by their teachers. As an addition to his earlier question of his teachers being naughty, he lists out things that he wants to know if his teachers have experienced. He asks if his teachers have also ever had the experience of not getting their spellings right. Like all children, he thinks that his teachers being a wise person, cannot make mistakes at all. His question can be taken in short as "How can someone who teaches me spellings and punishes me when I am wrong, ever have made the same mistake". The teacher, according to him, is the perfect person.
 
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Spelling mistake
 
He then recounts an incident where he has seen grown ups punishing children when they steal something. Pinching a chocolate flake in this sense means, taking away small bits of dark chocolate. They get punished even if it is not an entire cake or chocolate bar and is only a bit of chocolate. Children generally get excited to see the shiny bits of choco flakes placed as a decoration on top of a cake or ice cream. But since it is considered as bad manners, they are punished by making them stand in the corner of the room. It is a common punishment given to children to reflect on the mistake they made. The child is supposed to think about his mistake, what made him make that mistake and then regret about it.
  
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Chocolate Flakes
 
This stanza also talks about how children are often punished for their trivial mistakes rather than being guided. He wonders if his teachers have also been punished like that for such simple things in life. The stanza also reflects on the poet's personal life as he himself was punished several times because he could not get his spellings right.
 
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Child facing wall as punishment
 
Meaning of difficult words:
 
SI.no
Words
Meaning
1
RelatableAble to relate or have experienced the same feeling previously
2
Pinching a chocolate flake Stealing a small bit of chocolate from a decorated cake or chocolate
3
RegretFeeling bad for making a mistake
4
TrivialVery simple, not very important
Reference:
National Council of Educational Research and Training (2006). Honeysuckle. Where Do All the Teachers Go? - Peter Dixon (pp.67- 68). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.