Weed-out is a really bad way to look at teaching. It puts people in the mind set looking for excuses to get people to fail. The attitude should be teach-in.

If someone passes your entrance tests then in most cases if they fail either you failed to develop the ability that you decided they had, or your entrance test was wrong.

The UK military realised this a while ago and describing any activity as being 'weed-out' is a big no-no.