A 2 minute time out for him, with the computer/book still available after might be better - get him to demonstrate he can be calm but not pull the plug, which sounds like it is too severe, and putting a dent in his learning.
Good luck! We have similar issues here with ds9 wanting help, but stopping me every 3 seconds during an explanation so he can try again/take a shortcut/make a guess, which just makes the whole thing take longer.

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