A number of my less-able students or those with short concentration spans have difficulty settling in lessons. I meet them at the door at the start and give them a piece of paper that contains a settler activity. This might be a word search to introduce new vocabulary, a crossword to recap definitions from the previous lesson, or a code-breaker to pick out a point from previous work. (A useful source is Puzzlemaker at http:puzzlemaker.school.discovery.com ) The students immediately start work. By the time they have all arrived, most of the class are already engaged with the activity and, most importantly, are not distracting others or causing mayhem.
Instead of having to draw the class to attention to begin their lesson, I have students who have already completed an activity focused on the subject and are keen to continue with further tasks. If students don't finish the settler, they can return to it at odd gaps in the lesson, ensuring that they are still working and not distracting others.
David Pratt, science teacher, Keswick School, Cumbria