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At school I learnt were 5 vowels (a,e,i,o&u). I spent 30 years (+) with this information.

Some posts on this forum have asked for names and words with no vowels. The common answer has always been words with Y. Cry - word, Kyle - name. Somebody then posted that y was a vowel and thought that people thinking otherwise was ill-informed. My tutor (I'm doing a CELTA course) was explaining spelling and vowel sounds. Gave examples of stop becoming stopped (CVC CVC). Then gave he example of Cry -Cried when moving from the base form. (Yes we were doing past tenses/narrative speach). Given the comments on this site, and the example I chose Y as a vowel - which I was aware is listed as a semi-vowel. I was told I was wrong. Is that because I am wrong? or because I would confuse rather than teach. I will ask my tutor but wanted to get comment and more information before requesting information.
Comments  
I hope I don't block you chance to get a better informed answer.

People write books renaming things and arguing about what things should be called. Most issues can be viewed from different perspectives.
In the end, these people manage to get along with each other.

The best policy is to do what the teacher says, especially if you hope to pass the course.
Dave Phillipsstop becoming stopped (CVC CVC)
You're talking about stop and stopped, the words. The rule for forming the past tense when Y is the last letter is different from the other rules for forming the past tense. Is that what you're asking about?
Dave PhillipsI chose Y as a vowel ... I was told I was wrong.
In what context did you choose Y as a vowel? Was it in a specific word? Can you be more specific? Who said you were wrong? Your tutor?

I think we need more details before we can comment further.

CJ
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Yes we did look at stop/stopped, and then followed that with the rule for vebs ending in y in the passed tense becoming ied rahter than yed. When discussing the rule for stop-stopped that is when she asked what the vowels were.

The words I thought of were cry, fly, try.

My tutor flatly said the y isn't a vowel, without any further information. I will ask her but didn't get the opportunity so thought that I'd ask others to in part their wisdom.
In English, we rarely have words with no vowels.
In your examples (cry, fly, try), only the "y" can be considered a vowel.
Ask her to pronounce them when a consonant has been substituted for the "y."

crt

flc

trb

Something is missing from your story.
When she asked what the vowels were, why did you reply, "cry, fly, try"?

When "y" begins the word, it's not considered a vowel.

youth
yellow
yolk
yawn
yogurt
yesterday
yell
year
yarn
Yankee

Notice that all these words have "other" vowels in each syllable.
Dave Phillipsshe asked what the vowels were.
You might have answered, "A, E, I, O, U, and sometimes Y". There's nothing to be done at this point except to discuss it with your tutor.
Dave PhillipsMy tutor flatly said the y isn't a vowel, without any further information.
I assume you are paying her for the tutoring, so if you want your money's worth, you had better not let her "say things flatly without further information". Ask more questions during your tutoring sessions and don't let her get away with saying foolish things. Consider a different tutor if you can't get any straight answers from her.

CJ
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Thanks CJ.

I should have said sometimes Y and she might have clarified better. I will discuss it with her tomorrow when I see her again.
As far as I know, there are vowel letters and vowel sounds.

In Italian, if someone asks you how many vowels (letters) there are, the answer is always five: A, E, I, O, U. I thought the same was true in English, but Wikipedia says the written vowels are A, E, I, O, U, and Y, and Merriam-Webster says they are A, E, I, O, U, and sometimes Y.
If you include the letter Y, why not include the letter W as well? The letter Y represents a vowel sound in words like "shy" or "say", and it's a semi-vowel in words like "yeah". But the same applies to the letter W too: it's a vowel sound (part of the diphthong) in words like "cow", and a semi-vowel in words like "wish". Now, it looks like Y is considered a vowel letter because it can represent a vowel sound on its own, in words like "shy" or "system". On the other hand, the letter W can't be a vowel sound on its own, if I'm not mistaken: it's always found together with other vowels, as in "cow", "new", etc.

Sooo... if your definition of vowel letter or written vowel is "a letter that can represent a vowel sound even if it's not combined with other vowels", then the vowel letters are A, E, I, O, U, Y - bad, bed, bid, bot, but, by.
If your definition is instead "a letter that can represent a vowel sound even when combined with other vowels", then the letter W would be a vowel letter too, and then you might also get in trouble. Why? Because one of the most common and most taught English varieties (British English) is non-rhotic, which means R's are often not pronounced. So, if you use this definition, you would have to consider the R to be a vowel (as in British "car", "fur", "here", etc.). Also, there would be exceptions: borough/though, bidet/chalet, yeah/fahrenheit... where G, H, and T could be considered vowels.
If your definition is "a letter that always represent a vowel sound", you'll face several problems, again.

It looks like the first definition in bold is the only sensible one, and that would make the letter Y a vowel letter. This is just my opinion anyway.

By the way, there is a game called "The wheel of fortune", and if it's the same as its Italian version, you should be able to "buy" vowels. In Italy, you can buy an A, E, I, O, U. Can you also buy a Y in the United States? I would guess not.