It would be so easy — and so wrong — to make this true story of a Maori chess champion who struggles with mental illness as he teaches underprivileged kids into a safe, simple, saccharine, uplifting story. But writer/director James Napier Robertson, who himself played hundreds of chess games with real-life speed chess champion Genesis Potini, trusts his story and his audience enough to give us a film that is refreshingly messy, even grungy, and therefore much more powerful.

The extraordinary actor Cliff Curtis is renowned for being able to play almost any ethnicity, one reason he was an affecting Jesus in the recent Risen. Here, though, as in “Whale Rider,” he has a chance to play the part of a person of his own ethnic heritage, the speed chess champion Genesis Potini, who had bipolar disorder. Curtis shows us that Genesis is a person first, not a group of symptoms. In a meet, wanting so much for the kids he has trained to have a chance to succeed, he cannot restrain himself from shouting encouragement, and we see how painful it is for him to feel like two people at once, the one who cannot control his impulses and the one who understands what he is putting at risk.

Robertson also gives us an honest, unflinching look at the community where Genesis has come, after being released from the mental hospital with a fistful of pills and the direction to find something to care about. The only place he has to go is the home of his brother, Ariki (Wayne Hapi), and Ariki’s son, Mana (James Rolleston of “Boy”). Ariki is a member of a gang that hangs out, gets high, commits petty and not so petty crimes, and spends a lot of time in not so petty macho posturing. He does not like having Genesis there and soon kicks him out.

Genesis sees a flier for a program that provides enrichment services for needy kids and decides that this will be the purpose that will help him maintain equilibrium. He volunteers — waking the director up in the middle of the night to offer his services, and against his better judgment, the director accepts, warning Genesis that if he shows up, he cannot let the kids down. Genesis impulsively (he does everything impulsively) tells kids who have never seen a chess game before that they will be competing at a big tournament in six weeks. Before they learn how to play, he lets each of them pick a chess man to take home as a totem, and to bring with them every day so that the set can be a team again. It makes them into a team as well. He uses the money Ariki gave him for rent to buy chess sets for the kids and he sleeps outside.

Genesis’ splintered reality and lack of impulse control may be advantages for speed chess. All of the possibilities are laid out before him but that does not make him hesitate. But chess is a game of rules and it provides a certainty, order, and mastery that Genesis and the kids he teaches can hold onto and build on. Mana has to decide whether he will follow his father or his uncle. Genesis has to try to be the man Mana and the kids need. It might get corny but for Robertson’s unaffectedly gritty settings and understanding that modest gains can be enough for checkmate.

Parents should know that this movie includes violence, child abuse, drinking, drugs, mental illness, and extreme poverty. Characters use very strong language.

Family discussion: Why was helping the children so important to Genesis? Why was having Mana in the gang so important to his father?

If you like this, try: “Searching for Bobby Fischer,” “Bobby Fischer Against the World,” and “Endgame”