The motion comes from the center out - upper arm first, then elbow, then wrist. Done first away from the instrument.
Student holds the stick of the bow with left hand and draws the bow.
Flexibility of the wrist is essential. The use of the full bow should also be encouraged. The concept of griping the string before setting the bow in motion is an important concept that must become second nature. This is of greatest concern when playing on the lowest strings, and is not much of a concern when playing harmonics or in the upper registers. The ability to contact the string.