We have all heard, read, and seen in performance that petit allegro has started to fall by the wayside as dancers and choreographers focus on ever-higher extensions, larger jumps, and more pirouettes. This is to an extent natural and necessary as costumes become more revealing and we learn more about the way the body works (movement emanating from the torso instead of the extremities). However, it is possible to train dancers (who become choreographers) to be more attuned to the use of the lower leg and foot while still giving them the ability to perform larger-scale movements.
Such training begins (as do so many things in ballet) at the barre. Movements such as battement fondu, battement soutenu, and rond de jambe en l'air that used to be performed almost exclusively with the leg at 45º (toes level with the middle of the supporting calf muscle) now are often performed almost exclusively with the leg at 90º or higher. The position of the working foot sur le cou de pied creeps higher as well, almost to a demi-retiré position, so that during battement fondu at 90º or above the dancer does not draw the foot from a true cou de pied position to retiré before extending the leg; s/he simply raises it to a very high cou de pied/demi-retiré and extends it from there.
It is not wrong to practice these movements at heights above 45º; indeed it is a necessary part of a dancer's training, but it should be more the exception than the rule. Those three movements (along with battement frappé, which does not usually get distorted because it is difficult to raise the leg high while maintaining a strong, sharp movement) form much of the basis for petit allegro. For example, pas assemblé is a battement soutenu at 45º with a jump, and pas ballonné is essentially a jumped battement fondu. It requires a very large jump to perform rond de jambe en l'air sauté at 90º, and that would alter the timing and accents of most petit allegro combinations; therefore that step is more suited to grand allegro.
When practicing movements normally done at 45º, it is helpful to make sure they are done correctly. The foot sur le cou de pied must truly be on the neck of the foot, not on the calf muscle, and in raising the leg to a higher position such as demi-retiré or retiré (retiré position is different from battement retiré/raccourci, which may finish with the working leg in retiré, demi-retiré, or sur le cou de pied positions) one must take care to always pass through a true cou de pied position.
Pirouettes, too, can be useful in helping dancers become used to working with the legs at 45º and thus developing a greater awareness of the lower leg. Often, students first learn pirouettes from 5th or 4th position at retiré or demi-retiré height. When they learn grands pirouettes, AKA pirouettes in open positions, they generally start learning them at 90º. However, pirouettes sur le cou de pied without movement of the arms are useful even for advanced students to learn the appropriate action of the back muscles during all pirouettes, and students who can hold the working leg solidly at 45º but who are not yet able to do grands pirouettes at 90º can learn pirouettes in open positions at 45º. In fact, this would probably help them advance more quickly to pirouettes with the legs higher because of the control required of the back muscles.
I advocate for a greater focus on allegro during ballet class (and lengthening the standard class time to 2 hours instead of 90 minutes, but that is another blog post). A very common ballet class format for jumps is a "warm-up" combination consisting of small temps levés in 1st and 2nd positions as well as changements, then a "petit allegro" combination with assemblés, jetés, glissades, and pas de chats, then a "grand allegro" combination with grandes sissonnes, grands jetés, and jetés entrelacés (AKA grand jeté en tournant). I prefer a more gradual approach.
After the "warm-up" combination, one might do a combination of assemblés and small entrechats to reinforce the stabilizing muscles of the torso. This could be followed by perhaps two or three combinations involving small jetés, ballonnés, ballottés, emboités, ronds de jambe en l'air sautés, larger turning jetés, brisés, small cabrioles, small sissonnes, larger entrechats, and échappés. These would provide a transition from petit to medium (moyen?) allegro, for which one would do larger sissonnes, échappés, entrechat-six, and ronds de jambe en l'air sautés at 90º. Then, finally, a grand allegro with grands jetés, grands sissonnes, grands échappés, entrechat-six de volé, double tours en l'air, large cabrioles, fouettés sautés, &c.
Obviously it is not necessary to strictly pigeonhole every step as either "grand allegro" or "petit allegro" and there is no need to specify precisely where a step ought to occur in the progression of classroom exercises. Mixing and matching steps teaches students to handle a wide variety of choreographic styles with ease and grace. I provide the above paragraph to demonstrate the idea that allegro need not be rigidly broken up, that it can/should instead be a seamless progression of ever-larger and more complicated movements.
Finally, I realize that the negative examples I have provided above are not representative of everyone's experience and that many teachers are working against such technical mistakes and misplaced attention. There is much good training as well as bad and mediocre that occurs every day, and I provide examples of bad training so it may be seen, recognized, and corrected. I realize that bad training is not mistakenly exalted everywhere.