Viola vs. violin teacher for beginner violin students
For young violin students (8 years old) who are still relatively at beginner stage (Suzuki Book 3 - learning songs like Humoresque), does it matter that they are learning from a teacher whose main instrument is viola instead of violin? At what point is it crucial that the student switches to a violinist teacher?
A this stage, it doesn't really matter as long as the teacher is good. I would switch to a teacher who is really good at violin by the time he reaches around Bach A Minor concerto level or higher. That said, some teachers even voluntarily transfer students to another teacher if they think it's a good idea.
It depends how accomplished the teacher is at playing the violin. Many professionals routinely play both, even if their primary job is in one or the other.
So many factors! The two main ones would be the experience of the teacher on violin -- if he/she played up to a high level on violin before moving to viola, he/she should be fine. The other would be how serious your kids are or how serious you are as a family. I had one child who was extremely serious by book 3 and I never would have put him with a violist as a teacher. My other one would have been fine.
My wife was a violist and had great success with beginning violinists. But at a certain point, she did send them on to other teachers.
At this level, the technique for both instruments is virtually identical. There is no reason why someone who is primarily a violist would be an inferior teacher (except for unrelated reasons) than someone who is primarily a violinist until a pretty high level. I'm primarily a violist who also teaches violin. I typically send students on to a violin teacher when they reach the Kabablevsky Concerto level (or around there, sometimes earlier), as I didn't study that much violin repertoire beyond that very seriously. I have a colleague who didn't study violin at all who sends their violin students on after they finish book 4. I would maybe ask your child's teacher at what point would they send them on to a violinist (if they do), as long as a teacher knows their limits (some violists have studied violin to such a high level, they may not need to send on the average child student), you should be fine. In Suzuki teacher training, the viola audition allows you to take training for the violin books up to book 4, so the consensus among Suzuki teachers would seem to be that the technique is essentially the same up to at least book 4.
Most viola teachers themselves studied violin up through a certain level when they were kids, often somewhere between Kabalevsky and Mozart-3 and Bruch levels. I don't see the harm in asking the teacher about their background on the violin. "Did you start on violin as a child and if so how far did you get with it before you switched over?" That's not an insulting or offensive question, I don't believe.
There are points at which the techniques differ some, but the basic technique is the same for both instruments, and, if the teacher is good and inspiring, I am not sure it matters at the early stages which is her/his primary instrument.
I am a violist who plays and teaches both. To over-simplify, the viola is harder on the left hand, while violin needs finer bowing. I have actually earned more money playing violin than viola! My French friends link this to the way the British like driving on the wrong side of the road...
I'm happy with a violist (who afaik has never played violin) as my violin teacher, although I don't know how much ricochet she ever uses in her professional playing.