One of the most exciting moments of my junior-high-school career was stepping into my first-ever foreign-language classroom. While foreign language studies had a reputation for being tedious, I was nonetheless thrilled at the idea of being able to communicate with people from a different, seemingly more exotic part of the world. We were allowed to choose between French and Spanish, and I picked French because it seemed more “glamorous.”
Excited as I was to learn a new language, I was still shocked to find out that every word was either “masculine” or “feminine.” Livre, “book,” was masculine, but bibliothèque, “library,” was feminine. It made no sense. Was Madame Goldstein playing a cruel joke on us? No, it said so right in our French textbook. Eventually I came to grips with the idea of gendered words, but I always wondered why a language would need such a seemingly arbitrary construct. What possible use could assigning genders to words have?
In the decades since I first encountered the French language, researchers have begun to come to a consensus on the utility of gendered words: they help listeners to predict what word is coming next, and therefore aid comprehension. For example, “où est le livre?” means “where is the book?” and “où est la lingerie?” means something entirely different. It could be extremely important to distinguish between the two possible phrases, if, say, they were whispered in your ear at a crowded party.
Studies have found that native speakers of languages with gendered nouns are quicker at identifying objects with different-gender names than the same-gender names. For example, if a Spanish speaker was presented with a picture of a ball (la pelota) and a shoe (el zapato), then she would react faster to the phrase “Encuentra la pelota” (find the ball), compared to when the ball was paired with a cookie (la galeta). “La” immediately distinguishes a pelota from a zapato but not a galeta.
Casey Lew-Williams and Anne Fernald wanted to know when this difference begins to develop in children. So they located 26 three-year-olds, all recent Mexican immigrants to the U.S., native Spanish speakers who were exposed to Spanish at least 85 percent of the time. The children sat on their parents’ laps in front of two computer monitors, each of which displayed a picture of one of eight objects. Half of the objects were masculine (zapato, carro, pájaro, caballo), and half were feminine (pelota, galleta, vaca, rana). A recorded voice asked the child (in Spanish) to point to one of the two objects. Half the time the objects were same gender (masculine/masculine or feminine/feminine), and half the time they were different genders. The parent was blindfolded and wearing sound-masking headphones while their child participated. Then the kids were taken to a play area while the parents completed the same task. Here are the results:

The graph shows the portion of time the study participants spent looking at each object, for each moment following the point where article el or la was spoken. The black dots are for different-gender words, and the white dots are for same-gender words. As you can see, when different-gender words were displayed, both adults and children responded significantly faster than when same-gender words were displayed.
So even three-year-olds, with working vocabularies of only 500 words or so, appear to use the gender of a word to help recognize the word faster.
Interestingly, similar studies have been done on fluent second-language speakers, and the effect is not found. The advantage of gendered nouns seems to be limited to native speakers of a language — and this study suggests that advantage is acquired quite early in life.
Lew-Williams, C., & Fernald, A. (2007). Young Children Learning Spanish Make Rapid Use of Grammatical Gender in Spoken Word Recognition Psychological Science, 18 (3), 193-198 DOI: 10.1111/j.1467-9280.2007.01871.x