How to fix early arm bend?

[Smolandski]

Am trying to teach my son how to do Power Cleans, he is one of those early arm benders. He has a problem getting the "don't bend your arms early"...

Do you have any thoughts or advice on how to fix this?

Thanks in advance!

[Mark Rippetoe]

I usually just yell. If that doesn't work, I hit him with a board I keep here for this purpose.