The official Conservative line is to trust teachers' judgment but that has not prevented Mr Johnson, who may one day dictate education policy, from voicing his feelings. He speaks out this evening on Teachers' TV, a Government-funded digital channel.
"What we had and what I think needs to be brought back into education is an absolute ruthless instruction in grammar," he says.
The MP reminisces about studying classics at Eton. Each morning before breakfast pupils would sing grammatical rules until they knew them by heart.
"People don't do that any more and why not? Why can't we have grammar?" he says, thumping the table. "Why can't we have right and wrong answers again? Why not? Because it's all bollocks.
"All the teachers watching this who are going mad with indignation should know we have got to get back to right and wrong answers - and grammar and spelling and punctuation. Yes!"
Mr Johnson later adds that he is being "slightly hyperbolical, but basically serious".
His interest in politics stems from playing God in a school play. He felt "like some minister introducing some terrible bill to give schools trust status or something".
He said he had a broad understanding of the state system.
"At Eton I was the beneficiary of a scholarship endowed by Henry VI," he says. "If that is not state education I don't know what is."
School Days is on Teachers' TV tonight at 6.30pm