The Employee should recieve regular feedback during their probation period. This can be done informally, but if there are any concerns, these should be documented with an action plan.
At a minimum, the employee should recieve a formal written review after 3 months and again at about 5 1/2 months.
Failing someone in their final probation review should not be a surprise. As a result of feedback provided, they should know if their employment is going to be confirmed.