Setting a play in a night school for comics is a terrific theatrical concept, an easily imagined field day for actors. So it’s no surprise that — in this revival of British playwright Trevor Griffiths’ acclaimed 1975 work — the ensemble cast triumphs, particularly Jim Dale as the earnest teacher, and Raul Esparza as a bitter performance artist whose style is 10 steps ahead of the curve. But Griffiths has a lot more in mind than meaty roles. He’s written a highly serious play about comedy, driven by fierce working-class anger and passionately argued issues of integrity. It goes straight to the heart of what’s funny and what’s not — leaving us rousingly unsettled.