A high school student got lit up with a Taser during a tense encounter with a cop on an Atlanta school bus … and the disturbing moment was caught on camera.

The clip shows things spiraling fast — 18-year-old Lanier Johnson-Hunt refuses to get off the school bus, despite repeated warnings from a school resource officer that he’ll be tased … and after a brief scuffle, the threat turns real … with the Taser deployed at point-blank range, right on the teen’s chest, leaving him screaming in pain.

Fulton County Schools claim the chaos kicked off after a new bus driver thought the teen didn’t belong on the bus with other Langston Hughes High School students — adding they’re fully investigating the confrontation, which occurred last Thursday, according to WANF-TV.

Lanier, meanwhile, tells local media he’s furious — slamming the officer for tasing kids when they’re supposed to be protecting them — and he’s now hired high-profile civil rights attorney Harry Daniels, who says his client was just trying to get home to help care for his autistic brother.