The thinking skill of comparison and contrast begins by noting differences and similarities and then moves into deeper comparative processes.  Renowned educators Robert Marzano, Debra Pickering, and Jane Pollock (2001) compiled  available research on effective instruction and found that strategies that engage students in comparative thinking had the greatest effect on student achievement, leading to an average percentile gain of 45 points. More recently, Marzano's research in The Art and Science of Teaching (2007) reconfirmed that asking students to identify similarities and differences through comparative analysis leads to eye-opening gains in student achievement.

The ability to break a concept into its similar and dissimilar characteristics allows students to understand (and often solve) complex problems by analyzing them in a more simple way.  When comparing and contrasting, students must use relevant evidence from the text to support their points in writing and speaking, making their reasoning clear to the reader or listener. Students can utilize annotation, highlighting, and other engagement strategies to identify and extract pertinent details and evidence that contribute to the comparison at hand.

Although comparative thinking is a natural operation of our minds and is essential to learning, most students have a difficult time making use of comparisons in school. There are various instructional strategies to help students navigate the processes of comparing and contrasting, and research notes that graphic forms are a good way to represent similarities and differences.  However, a Venn diagram or other graphic should not be the end product of the compare and contrast experience; they are simply a means to organize ideas and evidence. Ultimately, students should be able to articulate in writing or speaking their conclusions based on the comparisons with evidence.

ASCD Article on the Strategy of Compare/Contrast 

Click here for an explanation and sample lessons utilizing the research-based process for comparing and contrasting.