Q: I’m used to flow yoga classes—why are Iyengar Yoga classes so “choppy”?
The flow classes that many people are used to taking are most often based on some version of a sun salutation with other asanas (poses) inserted which provide for “flowing” movements from one pose to another. While you will experience sun salutations, vinyasa (series of poses connected in a kind of flow) or jumpings in Iyengar yoga classes, it is not the greater part of what we provide. A good flow of sequencing, however, is a distinct feature of Iyengar yoga classes. Each asana taken has some purpose within the larger framework of the class. It could be that the action of one pose helps to understand the action that is required in many of the other asanas. It could be that a pose gives relief from another pose such as taking a twist after forward or backward extensions. Although the class may seem choppy because we have to stop to watch a demonstration or set up props, the class sequence itself is designed for an overall effect which is holistic. It could be an energizing sequence, a quieting sequence, back care sequence, focus on hip work or all category of asana sequence—the list goes on— but it will end quietly as the pieces of the class are pulled together into one.
We tend to “teach” classes rather than “lead” classes, though, again, you may experience a “led class” from time to time. In the teaching process, the teacher must see that the students understand the work or the key actions that are being cultivated. This requires that we spend some time demonstrating for clarity purposes. When the student is able to see and not just hear the instruction, he/she can get a better grasp on what is being taught. Iyengar yoga embraces a tremendous diversity in sequences, approaches and speeds in a class. For example, Geeta Iyengar has been known to teach only 6 asanas in a two hour class with great precision and refinement, and she has also led classes that were so swift that 108 asanas were performed in the same two hours. If you are considering taking on Iyengar Yoga practice, it is good to hold off judgement until you have tried several classes for this reason. Iyengar Yoga classes also offer a great variety of poses and variations on classical poses to suit every individual. We change things up so that you do not get stuck in habitual or mechanical performance of the asanas.
Iyengar Yoga teachers encourage their students to develop a home practice of their own. Yes, come to classes and then take what you’ve learned home and practice it. Ideally, yogasana practice is individualized to the need of each person on any given day. Therefore, the teacher is giving you some “samples” and tools for practice at home. Classes also provide some momentum or inspiration to take the practice on personally, to make it one’s sadhana (spiritual practice). You will gain some different boons from practicing on your own. Not everything that you do in class may be 100% suitable to you today, but there may be some things in class that you found particularly helpful for your sore lower back or shoulder, or that helped you to raise the energy when you were feeling dull. Play with those things at home. People who enjoy the “flow” classes out there can also benefit from Iyengar yoga practice as some more refined instructions on the performance of the poses in the flow are given. You can use those refinements in other class settings to protect yourself from injury, and also get to the quiet place of repose in the practice.
There is a great depth to yoga practice beyond the stretching and strengthening that is commonly attributed to yoga. It is so much more than a fitness regimen. The outer practices of ethical principles and inner observances of the yamas and niyamas (see Light on Yoga by BKS Iyengar) also have an opportunity to come through in Iyengar yoga classes. We do want to move — it feels good! Sometimes we move quickly through the asanas to develop mobility and other times we take it slower to work on stability or more accurate alignment. BKS Iyengar has said that “action is movement with intelligence”. As teachers we aim high, we want the student to create those bodily actions with intelligence and awareness. We are, in fact, training the mind through the body. We are using specific points of the body to focus on, to concentrate on. It is a way to persuade the unmanaged mind to become one-pointed. The mind is used to being scattered and jumping quickly from one thing to the next. Concentration is the 6th limb in the aṣṭāṅga yoga elucidated upon by Patanjali, and it is the beginning of the inner yoga practices. Concentration, when unbroken, becomes meditation. The breath as an excellent object to focus on, is common to this and many other styles of yoga practice. By teaching students to zoom in on particular areas in the body (or the breath) we are making more and more connections of mind and intelligence with body and prāṇa. As more and more subtle connections are made, the refinement of alignment that accompanies this style of teaching and practice leads to “meditation in action”, says BKS Iyengar.
A few words of wisdom from BKS Iyengar:
Never perform asanas mechanically, for the body stagnates. 
Use your intelligence to control the body before starting the movements of the body. In the beginning, the brain moves faster than the body; later the body moves faster than the brain. The movement of the body and the intelligence of the brain should synchronise and keep pace with each other. 
While performing the asanas the brain should be watchful and alert to direct the movements of the body. Activate the body, relaxing the brain.
When your posture is imbalanced, the practice is physical; balanced asanas lead to spiritual practice. 
 Iyengar: His Life and Work, BKS Iyengar. p 497
 ibid p495