Officers in Texas displayed startling belligerence at times, grabbing or tackling students a fraction of their size over misconduct that often appeared to be minor. Children in elementary school, including one as young as 6, were handcuffed. Teenagers were arrested, charged with crimes and even jailed. In the most extreme cases, they wound up in hospitals, bruised or concussed, after being body-slammed or shocked by Tasers, which are prohibited in the state’s juvenile detention facilities but allowed in its public schools.