"Tarjetas de Boca" or "Boca Cards" are incentives or rewards that I use in class to encourage students to participate, whether it's just answering a question in Spanish or working in a group to figure out the correct response with others.
"Boca" means "Mouth" in Spanish- and since my goal is have all of my students speaking in Spanish, "Bocas" seemed like a good theme. Each card has a picture of a "boca" on it. If you were in my classroom you would see me walking around constantly and handing them out each time a student participates in the target language.
Students collect the cards and save them for tests and quizzes. 5 cards is equal to 1 extra credit point on a test or quiz. Some students use them each week or two (with 1-3 extra credit points on average) while others like to save their cards for a more difficult test or for the end of the year. The record for the most boca points ever earned by a student at one time is 68!
I first learned about using a technique like this from one of my professors at UMASS Amherst (Tiesa Graf). I was observing one of her classes and she created something similar, calling them "microfonos" or "microphones" (with pictures of microphones on each card). Her students were permitted to use these cards in exchange for a night off of a homework assignment.
Whether it's 6th graders or 12th graders, students LOVE getting the opportunity to collect these cards and earn extra credit points!