A Long Island school-bus driver was hit with a drunken-driving rap yesterday morning after crashing his vehicle during a field trip and injuring a 12-year-old passenger, cops said.

James Sommer, 47, of Massapequa, was transporting a busload of Plainedge Middle School students to a laboratory in Cold Spring Harbor when he backed into a large tree limb and lightly injured the child at around 10:15 a.m., police said.

Sommer was arrested at the scene and charged with driving while impaired by alcohol.