Teach graphing and percentages to your eighth-graders using a circle graph activity. First, instruct your students to take a survey of their class. Follow these rules: Each person must be accounted for, even if in an "unanswered" category, and the question must show mutual exclusivity, meaning one person can't answer a question more than one possible way. For example, your student might ask: How many articles of clothing are you wearing? Instruct your students to create a circle graph, or pie chart, which shows the results of the survey. Circle graphs, according to information from the University of Illinois, represent parts of a whole or percentages.
Bar graphs compare sets of information, specifically the "amounts or frequency of occurrence of different characteristics of data," according to Syracuse University's Self-Instructional Mathematics Tutorials. For a bar graph activity, find three different pieces of information that represent the number of times something occurs per set. For example, choose the number of times students of each grade level go to the library on average.
Line graphs compare two sets of data in such a way that a student can predict what comes next. Additionally, line graphs tend to represent a change over time. For a line graph activity, instruct your students to record a daily occurrence in their lives. For example, your students might collect information on how many minutes per day they spend on Facebook. After a week or a month, plot the information into a line graph and predict usage during the next month.
Line graphs give false information with errors in data. Create a lesson that teaches your students to look critically at information they are given. To do this, take a line graph from a previous lesson. Tell your students to circle the first number to the far left of the graph; label this number "A." Then circle the next number to the right of A which exceeds A; label this number "B." Continue moving to the right, circling and labeling each number that exceeds the previous circle's number. Instruct the students to plot only circled numbers and to create a line connecting them all. Notice how this graph only shows an incline, without any regard or mention of dips or declines.