Print it out and laminate it. Give to each student in the class that has a problem blurting out at inappropriate times. Have students put a check with a dry erase marker or use little pieces of post it notes in each box. As students blurt out erase or take away the post it for one box. Students keep on their own desk so they are seeing that blurting out has consequences. Give student an incentive/goal for keeping a certain number of boxes at the end of the class or day! Students love this and it works really well!