I almost never give grand pile at the barre other than in 2nd until I’ve been working with young dancers for at least a few years and I know their technique is ready for such a complex movement. Even the pre-professional dancers I’ve trained often lack the exposure to cross training required, or have been taught in a manner that doesn’t support this deep knee bend. There is, of course, controversy with other teachers over when to begin the instruction of grand plie. But I feel initiating the learning of plie first in a non-weight bearing position and then in the center improves both the understanding and the mechanics as well as prevents ‘sitting’ into those vulnerable knees.