Yoga is healthy. If the school is doing it for that reason and NOT for religion, then they're fine.
Physiological benefits: blood pressure decreases, cardiovascular efficiency increases, ********* function normalizes, excretory functions improve, joint range of motion increases, dexterity skills & reaction time improve, posture & sleep improves, and musculoskeletal flexibility & joint range of motion increase.
Psychological Benefits: anxiety & depression & hostility decreases, concentration improves, it improves your mood, attention, concentration, and memory.