When we say Krishna Consciousness is a science, what does it mean?
In modern science, normally, when we test any theory, first the scientists create what we call a null hypothesis. A Null hypothesis is one type and a prevalant method of testing.
A Null hypothesis is basically the opposite of the original hypothesis. So to begin with, normally, the burden of proof is on the researcher to prove that there is some sought of association or connection between the variables tested. After collecting evidence, the researcher will either reject the null hypothesis or fail to reject the hypothesis.
For example, low education levels lead to low socio-economic status. This is the hypothesis. Now the null hypothesis will be that there is no relationship between low education level and socio-economic status. The researcher will collect evidence to either reject the null hypothesis or will fail to reject the null hypothesis.
Similarly, coming back to Krishna Consciousness, the hypothesis is - Krishna is the Supreme Personality of Godhead. The null hypothesis will be that there is no connection between Krishna and His position as the Supreme Godhead.
Then, we collect evidence to test. The only difference between material and spiritual science is that evidence in material science is collected externally such as in a lab, or inside the ground or in the sky or in a community etc. In spiritual science, the evidence is internal inside our heart. This is the big difference. Nevertheless, there is evidence. Hence this collection of evidence internally in spiritual circles is called self-realization. Therefore as we practice the methodology (chanting and serving) of collecting evidence (purification and self realization), we will eventually "realize" Krishna as the Supreme God and I as the servant.
This can happen this life time or multiple lifetimes after depending on the researcher who takes to this process with due diligence and proper execution of methodology (chanting and serving).
Therefore, to conclude, just as in any science there is literature and practical experiments. Similarly in Krishna Consciousness we have vast literature in the form of Bhagavad Gita and the like and practical experiments of which primary is chanting followed by humble service. Studying the literature and executing the practical aspects of the literature will lead the researcher to finding evidence and so one day can transit from informed faith (hypothesis/theory) to fact.
My journey as a researcher is in this continuum of going from informed faith to fact that Krishna is Supreme God!