What is the minus bat drop required for seventh and eighth grade Junior High Baseball?

There's no standard "minus bat drop" rule in Junior High (or any level of) baseball that's universally applied. Bat drop is a term related to the *length to weight ratio* of a baseball bat, and while youth leagues often have restrictions on bat length and weight, they don't usually express it as a "minus bat drop."

Instead, Junior High leagues typically specify maximum bat length and weight limits based on the age of the players and/or the specific league rules. These rules vary widely by association, state, and even individual leagues. You need to check the specific rules of the league your seventh and eighth graders are playing in to find the allowable bat sizes. Look for the league's rule book or contact league officials.