Why should kids not have there own desk

I think kids should actually, it keeps them separated from distractions by other kids. 

( I think the opposite, but to support your question, I'd say)

Kids shouldn't have their own desk because it increases the difficulty of collaborative group work. In the same table, you can all talk in a working manner. But you must make sure the children are capable of not talking about different conversations than learning conversations.

The last one is right