I am finally getting stronger in my quads.
In my initial teacher training we were told to not really work out the quads, "because they are strong anyway", and to focus on strengthening the hams. Well it has become clear to me as I took my first Classical session, that I was very weak in the legs.
Knee stretches, an exercise I never used to do, is becoming easier (well more doable). When I first did this exercise I nearly died. Really, I at least wanted to die. Since I first did this in an advanced (instructor) class, we did 3x10 reps; flexed back, extended back and knees off. If you have done this series you know what I am talking about.
In the beginning I even had trouble finding the position and maintaining it throughout was an impossibility. But I am getting there.
Knee stretches is still a killer, but now I am starting to like them. If your instructor is not giving this exercise to you, demand it. Instructors are reluctant to teach it because it is hard to teach. Also make sure you have some resistance, it should be hard.