They try to be objective. Those engaged in educational research look for consistency in experimental and test results. To them they know their results are reliable if successive impressions of a single investigator tend to be consistent with each other and objective if they are consistent with the impressions of other investigators operating under the same experimental conditions. An example of the consistency theory of truth is Idealism. Both suggest an external objective reality and probably an eternal immutable order of truth.
Pragmatists propose to test the truth of ideas.
Ideas, by themselves, are neither true or false, but become true or false when used to clarify some confusion that has occurred to obstruct educational practice. Truth is what works. Truth is literally verification. It is truth making. It is never perfect, unchanging or eternal, but always in the making.