Our eldest daughter (8yo) has been with Dr. Oster for 3 years, and our younger (5yo) for 1 year. I personally found Dr. Oster a bit intimidating at first, but the kids took to her from the beginning and just love her.
Dr. Oster is not for everybody. Here is a brief summary of Dr. Oster's teaching philosophy:
1. Start them early. In contrast to other teachers who don't want to take kids before age 7 or 8, Dr. Oster prefers to start them early, as early as 4 or even 3.
2. Don't baby them. Her driving philosophy is that kids can absorb much more than most of us think. Other teachers who will take young kids dumb down the lessons: no note reading, no expression, no regard for proper technique, etc. They will lavish praise on a child so long as she/he plays the right notes (and sometimes even if they don't). Not here. From the beginning, Dr. Oster's students are taught to read notes, key signatures, understand rhythmic notation, accidentals. They are taught proper form and technique. They are taught expression and dynamics. Apart from the piano instruction, they are required to take music theory classes once a week, which are taught at a college-level introductory theory course (circle of fifths, intervals and chords, etc.). They are required to take the Maryland state exams in music. And frankly, you will be amazed at what your child can pick up.
3. Heavy parental involvement is required. You do not drop off your kid, or let them practice by themselves. You will be sitting in the piano classes, to understand what your child is learning so you can guide them at home. You will be attending your child's music theory classes, helping her/him grasp concepts. You will be practicing with them at home, making sure they make progress. [So one positive byproduct is that parents end up learning a lot as well!]
4. It is hard work. There is no set amount of practice time; they will have to practice as much as necessary to make progress. That may be a little, or a lot. In our case, it is about 30 min to an hour every night for our 5-year old, and 1-2 hours a night for our 8-year old. Lessons continue throughout the year, with only a 2-week break. If you are taking a vacation, the clock does not stop; you will need to make up the missed classes and catch up to where you would have been without a break.
5. Dr. Oster sees herself as (and in actuality is) a co-parent of your child. These are more than piano lessons, these are life lessons. Your child will be learning: (i) how to focus; (ii) that she/he is capable of things beyond what most people expect; (iii) that hard work and discipline are essential for success; (iv) to be patient with themselves; (v) to have fun while working (otherwise they will quit); (vi) and to aim for excellence, not just to be "good enough."
6. Dr. Oster believes in immersion in the arts and culture. There are field trips to watch concerts and ballet performances at the Kennedy Center or Strathmore; and field trips to the Library of Congress, the Shakespeare Theater, and Hillwood Gardens.
7. Your child will be tested. To ensure progress, there are periodic tests where your child will be tested (via a recorded performance) on the piece she/he is currently learning: on notes and rhythm, on technique, on expression and dynamics, on tempo. Eventually she/he will join performances, which are not your typical recitals; these are concerts at serious venues (Constitution Hall, embassies, Kimmel Center, Ivy League universities, European concert venues, etc.) where concert-level performances are expected; these kids do not get a pass because they are kids.
Bottom line: if you believe in your child's potential, and are willing to put in the time and energy to bring it out, Dr. Oster is an excellent teacher. If you want casual piano lessons, you're better off somewhere else.