WordValeBoth IELTS and TOEFL reward the same thing: using the right word naturally, in context, at the right register. Neither rewards knowing a word's definition. That is why the classic 3,000-word list so often produces a candidate who recognises everything and can deploy almost none of it.
What the examiners actually score
IELTS's "Lexical Resource" band descriptors talk about range, precision, collocation and "less common" vocabulary used appropriately. TOEFL's integrated tasks measure whether you can paraphrase a source in your own words. In both cases, a word you can only recognise counts for nothing. A word you can use in a sentence, with the right preposition and the right tone, counts twice: once for range and once for accuracy.
Why lists underperform
Lists give you recognition. They are efficient at it. But recognition without context does not transfer to writing or speaking, and it decays fast. The words that survive to exam day are the ones you met inside real academic text, with a sentence attached, and reviewed on a schedule.
A routine that works
1. Read the kind of text the exam uses
IELTS Reading passages come from magazines, journals and newspapers written for an educated general audience. TOEFL uses university-level textbook prose. Read that, not exam word lists: long-form science journalism, editorials, encyclopedia entries. Twenty minutes a day.
2. Save every word you had to think about
Not just the ones you did not know. The ones you half-knew are where band scores move. Save the sentence too; the exam is going to test the word in a sentence, so learn it from one. On iPhone this is two taps.
3. Review daily, briefly
Spaced repetition at about three minutes a day is enough. Three weeks of it produces a working vocabulary you can actually use under time pressure, which is the whole point.
4. Produce, weekly
Once a week write two hundred words using ten of the words from that week's reviews. This is where recognition becomes use. It is also the best available rehearsal for Writing Task 2 and the TOEFL independent essay.
The words most worth having
Both exams lean on academic and formal register. Start with the Formal and Academic collection for the connective tissue of an essay, then the Debate and Persuasion collection for opinion tasks and Nuance and Precision for the "less common vocabulary" descriptors. For the science-heavy reading passages, Science and Nature and Technology and Computing cover the recurring ground.
A handful that turn up constantly: mitigate, ubiquitous, pragmatic, nuance, meticulous.