Second, Third, Fourth, and Fifth Chances

Behavior today was atrocious in all of the classes. I noticed that last week students were given several opportunities to correct their behavior with gentle reminders but that approach doesn't seem to have worked. How many chances should we give them in the beginning of the year to get their acts together? I've always heard that teachers, especially new ones, should be stricter and "meaner" at the beginning of the year than they are at any other time so that students know to take them seriously and adhere closely to the rules. That isn't what is happening here. I'm not sure if this outburst of disappointing behavior should be expected or if this is a product of our lax enforcement of the rules last week. Are we being taken seriously?