Are some elementary and secondary schools discouraging the enrollment of undocumented immigrant children?

The U.S. Department of Justice Civil Rights Division, the U.S. Department of Education Office for Civil Rights and Office of the General Counsel addressed this question in a "dear colleague" letter issued May 6, 2011. "Recently, we have become aware of student enrollment practices that may chill or discourage the participation, or lead to the exclusion, of students based on their or their parents' or guardians' actual or perceived citizenship or immigration status," says the "dear colleague" letter.
The letter cites Title VI of the Civil Rights Act of 1964, which prohibits discrimination based on such factors as race, color, or national origin, by public schools. It also cites Plyler v. Doe, the 1982 decision by the U.S. Supreme Court that held a state may not deny access to a basic public education to any child, whether that child is present in the country legally or not.
The letter and accompanying materials clarify that schools may ask for birth certificates to establish age requirements, but may not bar enrollment because a child has a foreign birth certificate. Furthermore, schools may not deny enrollment if parents refuse to provide a child's Social Security number.