Technology has become essential to middle school and high school learning, but a gap in access to the Internet between the rich and poor is leading to troubling disparities in education, according to a survey of teachers.

Students depend strongly on the Web to find information and complete their assignments. The vast majority of teachers say they also rely on sites such as Wikipedia and social media to find teaching resources and materials and connect with other teachers and parents, according to a survey released Thursday by the Pew Research Center.But three-quarters of teachers surveyed also said Google and other search engines have conditioned students to expect to find information quickly and easily and discourage children from using a wide range of sources for research, according to the report.

But even as many schools race to adopt tablets, e-readers and cellphones for course work, those technologies are more widely available to middle- and higher-income students and schools.

Half of all students in higher-income families have access to the Internet at home. The figure drops to 20 percent for middle-income children and just 3 percent of students from poor homes, according to the survey of 2,462 teachers by the Pew Internet & American Life Project in cooperation with the College Board and National Writing Project.

The growing disparity of Internet access is leading to a gap in performance, about 56 percent of teachers said. About seven in 10 teachers say their students now rely on the Internet to complete their assignments.

“Teachers whose students come from the lowest income households feel they are at a disadvantage,” said Kristen Purcell of the Pew Internet & American Life Project.