My HS English teacher was even more harsh (but effective) - every time someone said um, ah, like, or any other tic/pause word, she'd immediately cut them off. 'STOP.' 'TRY AGAIN.' 'NO.' etc. She was relentless, forced students to stop, calm down, gather their thoughts, and say it directly. Most students were cured in a few days, and the really bad ones a few weeks at most.