Peer Help and Expert Board is a great tool for centers or the LATIC (Learner Active Technology Infused Classroom).
If students need help while the teacher is busy helping other students, they can write their name on the help board so the teacher or peer expert can assist them in a timely manner. A student who has mastered key concepts and skills so well that he or she can explain them to another student can write their name on the Peer Expert Board for other students to refer to.
This is a poster that can be printed as an engineering print at Staples for a few dollars. Students can use chalk board markers or sticky notes to write their names.