(Modify and do what works for you)
I have students line up outside and I wait until they are all quiet. Classroom behavior is more important than a lesson that can be modified or done later. Noisy students are sent to the back of the line. Watching both outside and inside, I stand by the entrance. When students are ready I then say, " Please walk quietly and stand by your computer." If students run or sit down or are noisy, I say to them,"Please come outside." Then I whisper to them, "Would you like to do computers?" If they say no, I have a table with appropriate paper work for them to do that might include filling in the letters of a keyboard while the rest of the class does keyboarding or computers. If they say yes, I smile and point my finger at my head to indicate "Think," and invite them in. If students sit down or yell or touch their computers, I send them to the doorway to stand inside not outside. I tell them to count to 30 or 60 in their head and come back and try again. If they continue with misbehaving then I have a responsible student walk them to the office or back to their teacher with a note that I have written explaining the problem. Later, I thank and sometimes reward in some way the responsible student. (When students always expect a reward, I tell them that we do many things without always getting a reward.) As the students are standing, I explain the activities of the period. Days later, depending on the class, I might say, " Class, raise of hands, how many of you can come in and sit quietly without touching your keyboard or computer until after I give instructions?" If they all raise there hands, I say, "Let's try that next time." If problems start to arise we go back to square one.