My 8th graders drew Bohr models of atoms at the beginning of class every day for a week (until everyone in class could complete the task correctly).
Nothing promotes collaboration between students like the desire to "quit doing this over and over." I
I copied this page on two sides and handed one sheet to every students. I always began the lesson with Boron, then challenged students to draw larger and larger atoms. You'll notice from my example page I always had the students label the electron rings 2-8-8, always had them write the A=P=E rule and write out the equation for determining the number of neutrons. Just provide students with copy of the Periodic Table and begin practicing every day. My classes usually did 2-4 practice atoms a day. I'd project the practice sheet on the front board (or smart board) and have a student volunteers draw the correct Bohr model. By the end of the week, everyone usually mastered it.
A week later, I'd have them draw
Boron and Sodium again to make sure they had retained their mastery. As an additional task, I'd have them label the valence electrons,