Why is using dans le to indicate one’s in an actual dance class wrong?

Question

Accepted Answer

Hi Liz, 
If you are taking part in the dance class it will be -
Je suis en classe de danse

Answer

Hi Liz,
Where was this marked wrong Liz?

Answer

Hi Cécile. On one of the lessons dealing with using dans vs en: I’m in dance class. I took this to be a specific location requiring dans vs en. Thanks for your help.

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Great. Thanks so much.

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Hi, I had the same question on a quiz. The question was:

Je suis ________ cours de danse. Je te rappelle.

I put "dans le" as my answer and it was marked wrong. The correct answer is "en". Given the explanation from @Cécile, I can see how "en" could be an appropriate answer, e.g. "I am currently taking part in a class". But from what I can tell, the answer "dans le" could also be a valid answer, e.g. "I am currently in that place".