The teachers are somewhat responsible because it shows how well the students learn in that class. If the teachers do have good/ better teaching methods then the students should be able to do well on the test. If you can keep them wanting to learn and wanting to be in class anyone can pass.
A teacher who is getting their students to want to learn will generally have much higher scores than a teacher just giving the students the material and teaching in a boring way. No one likes to be bored, it it won't stimulate the brain to sit there not having fun while learning.
Every kid is teachable, no matter what learning disabilities a kid may have. Test scores do reflect upon a teacher's performance for some of it. The other part is up to parents--half of kids come from broken homes. Some parents simply don't have enough time or effort to devote their lives to their children. However, it is a teacher's job to prepare kids for standardized tests. Therefore, test scores do reflect a teacher's performance.
While test scores can sometimes be useful in determining what a student has learned, they can't be a sole-decider in how a teacher has performed. Some students don't test well, and may have learned things in a slightly different way than in represented in a standardized test. Teacher's performance should be looked at from a variety of angles, not just tests.
Test scores are one way of telling how well students are doing and as a by product, how well teachers are doing. But that only works in certain settings where there is enough support. When and where the resources in the classroom are few, teachers should be free to teach in any way that gets a youngster to learn.
Test scores do not reflect on teachers' performance. There are many good teachers who have very good teaching methods, but have a hard time when it comes to tests. In my opinion, tests are an evil method invented to prevent some potential individuals from advancing further. Tests only prove that one can do well under pressure and based on what they memorized, it does not necessarily prove one's performance.