I loved using the straw static electricity with my students because it seems "magical" and it gets them ansking lots of questions about static electricity.  I combined this with the "Balloons and Static Electricity Simulation" by Phet with follow-up questions and assessment that will help them gain an understanding of the interactions between positive ions and negative electrons.  It helps students see the reason for the phenomena that they observed with the straws.  Finally, I included an assessment question to bring the two activities together so that you can see what the students have learned from the activity. This will help you tease out any misconceptions or weaknesses in student-understanding that should be addressed in future lessons.