That may not be the real name of the theory which is about the completely hidden part of acculturation to gender roles, the part which is invisible. Other parts can be extremely visible (such as direct gender discrimination, religious rules about sex roles or examples like this intersection of race and gender in the treatment of black girls in US schools), but even those who are not subject to the avalanches of openly gendered rules may have been subject to the drip-drip experiences.
This is the idea that we are all slowly, slowly being filed down to a shape that will fit the hole the society has deemed acceptable for us, from childhood onwards. Those drip-drips are tiny events, not necessarily important in themselves, but as water dripping ultimately hones down a stone into a smooth pebble a continuous "rain" on us can have significant effects on the shapes we will take.
As an example of this, consider this study from Israel:
Beginning in 2002, the researchers studied three groups of Israeli students from sixth grade through the end of high school. The students were given two exams, one graded by outsiders who did not know their identities and another by teachers who knew their names.It's possible that all the teachers did was anticipate future developments (though what works against that is the absence of the reverse bias in English or Hebrew, areas in which girls are expected to do better than boys). I have not read the study itself to see how well the controlling of other factors worked. But even if that is the case, the drip-drip theory is likely to tilt things further in the anticipated direction.
In math, the girls outscored the boys in the exam graded anonymously, but the boys outscored the girls when graded by teachers who knew their names. The effect was not the same for tests on other subjects, like English and Hebrew. The researchers concluded that in math and science, the teachers overestimated the boys’ abilities and underestimated the girls’, and that this had long-term effects on students’ attitudes toward the subjects.
For example, when the same students reached junior high and high school, the economists analyzed their performance on national exams. The boys who had been encouraged when they were younger performed significantly better.
They also tracked the advanced math and science courses that students chose to take in high school. After controlling for other factors that might affect their choices, they concluded that the girls who had been discouraged by their elementary schoolteachers were much less likely than the boys to take advanced courses.
When you put that one drop into the pail gathering them at the root of your feet things start looking different. By the time you reach maturity you have been filed and sanded and honed by hundreds of similar small events. Some of them you will remember, most of them you have forgotten or never knew about.
It's crucial to point out that the people doing the honing or filing are almost always totally unaware of what they are doing. Any one of us could be holding that file or sandpaper. One observation study* of a Finnish daycare center found that the caregivers paid more attention to boys than girls, helped boys first (in dressing, say, which is not necessarily good for boys) and expected more sharing and controlled behavior from girls than boys. Dolls were assigned to girls first and cars to boys first.
When the caregivers involved in the study found out the results they were shocked. All those drips were unconscious, created by the way the society had filed and honed them in the earlier rounds.
None of this is an argument for a hundred-percent environmental theory of gender roles. But it is important to notice that the societal effects are often of the type discussed in this post and may be as invisible as gentle summer rain.
*Link in Finnish, sorry