How can 'common effort' 'help' someone 'teach other students' as stated in the attached image?

There is a student's feedback on a language school's FB page.

I am wondering how 'common effort' can 'help' someone 'teach other students'.

Besides, I am wondering if 'the Cambridge exam' should be re-written (either by omitting the article or by making 'exam' into the plural) since the exam's name had not been specified.

And how can a language school be "the key point" in someone's 'realisation'?

The student worked with other students. For 12 years. He is describing that as a "common effort" that helped him learn.

Now that he has learned, he can teach others.

The audience for this message obviously knows exactly what "Cambridge exam" he is referring to.

I would have said:

a 12-year voyage

Uncanny said:

I am wondering

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The English in that image you attached is poor and has mistakes in it.

teechar said:

The English in that image you attached is poor and has mistakes in it.

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I have tried to point out the ones I noticed. Please do the same.

SoothingDave said:

The student worked with other students. For 12 years. He is describing that as a "common effort" that helped him learn.

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No, it did not. He learned the language up to or at or all the way through the C2 level by enrolling in the school and getting the teachers' help.
We don't know how long ago it was and if he still remembers what he learnt in the past.
"Common effort" helps him teach. He may be teaching at the A1 level if he has forgotten most of what he had learnt before.

I thought you came here to ask for help. I see you understand it better than I do.

Uncanny said:

Bogdan: Perspectiva Centre was the key point in my realisation.

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That doesn't make sense here. I have no idea what he's trying to say.

Uncanny said:

We have bonded for a 12 years voyage

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He tried to use words above his register, and this is the result - vague and unnatural.

Uncanny said:

that helped me learn English at the C2 level,

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He probably means "that has helped me reach C2 level"

Uncanny said:

Now, I am glad to see that

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Again, he probably doesn't need all these words.

Uncanny said:

common effort

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I have no idea what he means by that.

Uncanny said:

helps me teach other students who wish to pass the Cambridge exam.

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I understand that part!

He doesn't immediately seem to me to be of a C2 level.