If whatever you are doing - detention, calling parents, using the office etc. - are working you will know almost immediately. You should find the behavior becoming less and less due to the intervention until it goes away never to return. If you find no change or it becomes less for a day or two then returns it should be a signal there is something amiss with the intervention. This could mean the method is not working because it is not being performed correctly, or it is being performed correctly but is the wrong method for the particular student.