To some extent, it's all about outcome. You can tell a class or a coach is good, i.e. effective, if the majority of students are getting better.
But there are ways to spot a class where the coach isn't making the optimum environment for this to happen.
Kids aren't moving
Especially at the very beginning levels, like tot classes, and Pre Alpha/Basic 1-2, what skaters need most is mileage, and the ability to push themselves to a glide. A beginner class where kids are standing around a good bit of time waiting for the coach, or waiting for the slower skaters, is a weak class. (sometimes waiting is okay, but it should be kept to a minimum). Get those kids moving!
Coach is constantly yelling at the kids to behave
This is not a sign of a "tough coach" or bad kids. This is a sign of a coach who doesn't know how to control a class.
In a class with two coaches, the coaches are spending all their time talking to each other
Two coaches? They should hardly ever even be standing together, let alone gabbing. One should be leading the class, one should be helping the outliers, or the criers, or supervising the speedy ones that made it across the ice first.
The "outlier" kids get no attention
The outlier kids are the ones at either end of the bell curve-- the really good skaters and the really bad skaters. A weaker coach will ignore these kids, expecting them to either learn on their own (the good ones) or learn to catch up (the bad ones). You can't give these kids all your attention, but a good coach will find ways to keep them with the class, and succeeding within their own needs and limitations.
There are lots of injuries
I'm not talking about falls. There are always falls in skating classes. But if some child is getting sent off the ice for first aid at every single session, something is wrong. Ask the teacher why so many kids are getting hurt. It should not be rare to make it through an entire session of beginning classes (through Delta), or more than one session, without having to get a single bandaid or ice pack.
The coach talks a lot
It's not a university lecture, it's a skating class. Adults love this--standing around talking is way less scary than actually moving. But even they have to move eventually. If the coach is talking without the kids moving for more than a few minutes of the class, it's too much. And you can see when it's too much, because they kids will start wandering off.
This is a tough one, but I would consider it a red flag. There should be one kid able to pass at every level.
Nobody passes, except the kids taking privates from that coach and his/her cronies
Yeah. Nuff said.
Coach only talks to those kids from the last example
Complain to management; ask them to come observe a class.
Coach never steps off the ice to talk to parents
Even in the most densely scheduled programs, at some point in the session (not necessarily every week), the coach should make herself available to the parents.
Coach doesn't know the kids names
If you never see the coach taking attendance, you can be pretty sure he's not going to know your child's name. I consider this actually insulting; it turns the child into a cog or a commodity. There are coaches at my rink who tell me I'm too tense because I take attendance. But I'll just bet those coaches are not getting hugs at the mall when their students see them there.
What bad coaching have you observed?