This qualitative case study uses observations and interviews to examine the
practice of differentiation by twelve collaborative middle school reading teachers in a
school that has shown a decrease in the achievement gap for students with disabilities on
end of year tests on state standards. Observations and interviews were analyzed to
determine the teachers‘ knowledge and application of differentiated instruction. The
results showed that four of the six teams possessed a comprehensive knowledge of the
practice of differentiation and the data available to assist in planning lessons. Some
differentiation was observed in each of the six classrooms.