In tonight's CBS movie "Thin Ice," a high-school teacher and her pupil are chastised and hounded by a community because they're having an affair. Given their personalities, it would seem more probable that they'd be brought up on charges of flaming dullness.

But if the lovers -- Kate Jackson as the teacher and Gerard Prendergrast as the student -- are too dewily pastel, the film (at 9 on Channel 9) is not at all as bad as one might expect. There's usually a redemptive authentic touch for every walk on the silly side of the script by David Epstein takes.

One can believe, perhaps, that in a small American town, the teacher and student would be considered slightly scandalous. Perhaps roughnecks would even slash the teacher's tires, as they do the film, and it's easy to imagine a pig-headed pack of hypocrites on the school board trying to deny Teach her rightful severance pay after they boot her off the faculty.

But hooligans who hang the teacher's kitty-cat? And then drop it off on her doorstep in very broad daylight? You half expect them to march her to the guillotine after that ludicrous touch.

Director Paul Aaron ("A Different Story") makes the best of the moments that do ring true, and gets the most out of a cast that also includes that royal personage Lillian Gish as "Gran," Jackson's cheerfully liberated grandma, and Barton Heyman, looking like a combination of Van Johnson and Charles Kuralt, as the lawyer who helps the lovers sock it to the school board.

Jackson, who was always too human for "Charlie's Angels," remains terribly appealing, if a trifle vacant around the eyes. She has a sweet scene with the kid soon after learning she's to be sacked; they hug and nuzzle in the downstairs hallway, and when Gran asks who's there from her bedroom, Jackson calls out, "It's my young man," her teary words muffled by his shoulder.

On paper it was just another lovers-against-the-world tale, but such touches as the Charleston, S.C. locations (crisply shot by Andrew Lazlo) and the fact that the lovers win out over hostility and stick together register as legitimately upbeat. "Thin Ice" may be a bit thick, but it is handily navigable.