Mockumentaries usually go for big laughs, but this one is a rarity. “Chalk” satirizes the high school teaching experience, to be sure, but while it has many funny moments, the humor is mostly dry, and much of the picture mixes the serious with the comic and is as poignant as it is pointed. That’s certainly due in large part to the fact that the writers Mike Akel and Chris Mass drew on their own teaching experience in devising the script.

“Chalk” also combines actors in the lead roles with actual youngsters and teachers, giving the ensemble an authentic feel, and keeps the leads from degenerating into mere comic caricatures, making the picture seem less send-up than a slightly exaggerated record of reality. And the fact that the piece was shot on video at an actual campus in Austin, with an absolute minimum of slickness, creates a truly documentary look.

The main focus of the film is on four staff members. The one most broadly written and played is Mr. Stroope (the boistrous, sometimes boorish Mass), a third-year history instructor whose command of the material is dubious (at one point he berates a couple of students for making him look bad by knowing too much) and frequently gets behind in his lesson plans, but runs his class with unjustified self-confidence and thinks so highly of himself that he castigates his colleagues for not doing their jobs well enough while blatantly campaigning for the school’s Teacher of the Year award. Close behind comes Coach Webb (the intense Janelle Schremmer), presented as a sort of minor-league martinet who tries to get the other teachers to adhere to the rules as closely as she does while starting up fitness classes. Webb also butts heads with Mrs. Reddell (gregarious Shannon Haragan, capable of showing real fire and anger as well as chirpy good will), a former music teacher appointed the new assistant principal, who finds the demands of the job eating up the time she’d prefer to spend with her family and the most fulfilling aspect of it being the days on which she’s called to substitute for absent teachers.

The soul of “Chalk,” though, is the figure clearly contrasted with Stroope—Mr. Lowrey (Troy Schremmer), an erstwhile computer engineer who’s taken the job of first-year history teacher. Over the course of the academic year covered by the picture, we watch him gradually transformed from a bumbling, inept teacher incapable of managing his class at all or gaining their respect to a slightly less klutzy instructor whom his students actually come to like—insofar as students are capable of liking teachers. It’s Lowrey, beautifully played by Schremmer, who exemplifies the difficulties teachers face in learning how to teach and how to deal with students (a sequence in which he gets into a nasty argument with one of his kids over a cell phone and then goes to talk with the boy’s mother is an absolute gem, and one feels a sense of real triumph when he manages to win a student-run bee in which teachers try to spell current slang words). And in the end it’s he who points up the dilemma so prevalent in today’s teaching profession: though he’s come a long way, Lowrey’s uncertain whether he’ll continue in the classroom, admitting at one incisive moment that he doesn’t know if he actually likes teaching all that much. Since by this time we’ve come to empathize with Lowrey so completely, the remark brings home at the close the significance of the note that begins “Chalk”—that fully fifty percent of high-school teachers leave the job within three years.

“Chalk” doesn’t tell us much about the students at what’s called Harrison High. We see them obliquely, from the perspective of the teachers—mostly as snide troublemakers or bored and unresponsive kids, sometimes as angry and dismissive (during that argument with Lowrey, the student calls him a horrible teacher), and only very occasionally as helpful or interested. And it certainly doesn’t suggest that they’re leaning a great deal, or being inspired by any of their teachers to set their goals very high.

That reflects the basic honesty of “Chalk”: it rejects the typical Hollywood scenario of troubled students who reach great heights in English, or math, or something else by reason of the determined efforts of some incredibly dedicated teacher who won’t be stopped by the derision of his or her colleagues. There are no such great triumphs here, merely the reality of the generally well-intentioned but nonetheless pervasive mediocrity that characterizes so many public schools nowadays. This might not be the high-school story most of us want to hear, but it’s a true one, and “Chalk” tells it with insight, humor, and an appropriate touch of sadness.