A chemist, exploring something, pours 1 part A into 1 part B, and the mixture explodes. The chemist can then duplicate this same process in a laboratory, under close to the same preconditions: the exact same amounts of material, the same temperature, the same bowl even (if it survives the explosion). And when this experiment is done enough times (enough to satisfy some "rules") the chemist can say, "This seems to happen all the time, at least under this conditions, so I would say there is reason to believe that under these preconditions (temperature, pressure, materials..) if you take 1 part A and put it into 1 part B, it will explode."
A "humanist," being a teacher in a class room (not that I am saying that is what a humanist is) can try some teaching method, and observe a good result -- let's say the students' grades go up for this one class, this one time. The teacher wants to test this out. Will it happen each time? So for the next class on the same subject, the teacher teaches the same way, doing the same things, with the new students. Assume for the argument that the students in class B also get better grades (better than what you might ask? And I would have to say, well, better than students taking the same class got before the teacher started this new teaching method, or better than another class, at the same time using the old teaching method); what can the teacher say? The teacher cannot say, "Under these preconditions..." because individual students make up the preconditions. These students are never the same, even if they have the same educational background, even if they have gone to the same classes, and have the same grades. Some students will read newspapers and watch news on TV, others don't care for news and only read novels. Some rarely read at all. There are many and varied influences on students.
Students are not like chemicals. They can not be reduced to molecular construction..no two students are the same. The teacher could say, if the teacher knew all the preconditions, "Under these preconditions (semester, daytime, temperature...) this class with the following students, Bill, Anna,... got a better grade average then this other class with the following students, Paul, Maggi.. And in another example, with these other students, the students, Betty, Ralph..., got a better grade average than Kathy, Mick...", but can the teacher say, "So from this, under the same preconditions, students following this new teaching method, will get better grades than students who don't?" I don't think so.. I would think that it might show that the new way of teaching is worth looking into, but for another teacher, the old way might work better.