As more than 55 million children and teens across the US pour back into classrooms this fall, a real-life experiment is taking place on whether schools can stay open safely amid the aggressive spread of the delta variant. 214 President Biden said he would do everything in his power to get as many students as possible back in school. But that promise is being tested by the highly transmissible variant of the coronavirus, which has infected more kids in the opening weeks for some schools than in all of last year while forcing nearly 1,700 temporary closures, according to Burbio, a data firm that tracks school reopenings.