And by recommended, I mean scientific research or recommendations from experienced language teachers.
Out of a daily language practice session, how many new vocabulary words can an adult foreign language learner be expected to learn on average? I understand that this obviously varies from person to person and from language to language, but I'd like to know if there are any general, average numbers, statistics, or expert opinions.
You can use any range you like, of course. But for me, the sweet spot is about 15 new words a day. If I’m focusing really hard for a short period, I can double that. Usually, though, I stick right to that 15-word range and enjoy steady long-term results. One of the most important things to keep in mind is that you rarely learn a vocabulary word the first time you see it, or even the first day you see it. You have to review a word again, and again, and again. I’ve seen estimates that say it takes seven meaningful exposures to really learn a word, but I wouldn’t be surprised if it’s closer to 20 or 30 exposures.
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I will save you a lot of my usual babbling and give you my personal opinion based on years of experience in foreign language learning right now: 30 minutes per day is the bare minimum. This is the minimum that you need to actually make continuous, consistent progress. It won’t be very fast progress, but it will be consistent and continuous.
Both sources refer to learning Spanish, so really about 15 words a day, with 30 minute or more practice sessions. The first source suggests that learning less than 15 words daily could be too slow, while learning more than 50 words a day could cause you to not remember the words.
I think it's also a safe bet to say that this works for any other language other than Spanish.
In 1995, James Milton and Paul Meara published the article "How periods abroad affect vocabulary growth in a foreign language", which reported on the effect of studying six months in the UK on the vocabulary size of non-native speakers of English.
Students whose native language is not English spent six months in the UK (on a Lingua or Erasmus scholarship), and their vocabulary size was tested both before and after their stay in the UK. Their average increase in vocabulary was 1326, which represented an annual increase of 2650 words. (This represents an average daily increase of 7.26 words. However, there was no follow-up test several months later, so final retention is not clear.)
There was one student whose vocabulary did not increase, and five students who scored worse in the post test. Milton and Meara write, "The growth scores varied from -900 to 3800, with an sd of 1058." So there is a lot of variability.
The researchers also found that this growth was four times as big as for students who stayed in their native country, who learn 500-600 words per year (with a much smaller standard deviation than the exchange students). However, the researcher also point out that it is not clear that the exchange students would have kept up the same growth year for a whole year (instead of the six months in the experiment). In addition, students with high initial scores progressed least; these were typically also students with high rates of vocabulary learning at home.
In an article by Rob Waring and Paul Nation from 2004 ("Second Language Reading and Incidental Vocabulary Learning"), the authors noted that (emphasis added):
Most research data we have looked at suggest that learners will learn about 3-6 words per hour of reading. If we assume that a student in school has 3-4 hours of exposure to English each week for 40 weeks a year, and one third of that is reading, this totals about 50 hours of reading per year, or vocabulary growth of between 150 to 300 words per year, not counting natural forgetting from the reading alone.
I haven't found any studies on vocabulary growth in Spanish as a foreign language, but I assume the results should not differ significantly.
