I have read a number of papers within the field of educational research where researchers simply used their own classes for testing. For example, they test one of their classes with a certain type of instruction, but leave another class without this instruction, then: (1) test which group of students did better and (2) collect student opinions about the lesson.
While I can understand why a teacher might conduct an "informal" study on their classroom, I cannot understand why this would regarded as publish-worthy research. It is possible that I am simply misunderstanding the benefit and purpose of publishing such studies?
Within educational research, is it regarded as acceptable practice to publish research which is only conducted on such conveniently available groups?