I would personally recommend correct tendus rather. In the pliés, the turnout is easy enough to 'feel', but my guess is that it's not in the plié that the turnout 'gives' but in any other closed position/movement. So, the tendu would be a good start (to assess when the heel leaves the floor and how, and how to turn the leg in the closed 5th, or to release the leg to degagé without letting that leg or the standing leg turn in).
It takes -for a start- an 'intelligent' understanding of what the correct posture is, and how the turnout works anatomically. Once this is understood, then the work 'physically' can begin. That is much easier once you understand how to 'turn' the leg out from the hip socket.