(AP) — As the morning school bell rings and students rush through crowded corridors, teenagers in one Portland classroom settle onto mats and meditation pillows. For 90 minutes, three days a week, they practice a mix of yoga, sitting and walking meditation, visualization techniques, deep breathing, journaling and non-judgmental listening. Mindfulness, yoga and meditation have gained popularity among Americans in recent decades, buoyed by studies showing their benefits to emotional, mental and physical health. Prison inmates, hospital patients and the U.S.