Critics contend that zero-tolerance policies like those in the Christina district have led to sharp increases in suspensions and expulsions, often putting children on the streets or in other places where their behavior only worsens, and that the policies undermine the ability of school officials to use common sense in handling minor infractions.

For Delaware, Zachary’s case is especially frustrating because last year state lawmakers tried to make disciplinary rules more flexible by giving local boards authority to, “on a case-by-case basis, modify the terms of the expulsion.”

The law was introduced after a third-grade girl was expelled for a year because her grandmother had sent a birthday cake to school, along with a knife to cut it. The teacher called the principal  but not before using the knife to cut and serve the cake.

In Zachary’s case, the state’s new law did not help because it mentions only expulsion and does not explicitly address suspensions. A revised law is being drafted to include suspensions.

“We didn’t want our son becoming the poster child for this,” Ms. Christie said, “but this is out of control.”

In a letter to the district’s disciplinary committee, State Representative Teresa L. Schooley, Democrat of Newark, wrote, “I am asking each of you to consider the situation, get all the facts, find out about Zach and his family and then act with common sense for the well-being of this child.”

Education experts say that zero-tolerance policies initially allowed authorities more leeway in punishing students, but were applied in a discriminatory fashion. Many studies indicate that African-Americans were several times more likely to be suspended or expelled than other students for the same offenses.