You won't always have a calculator in your pocket

What actually happened

This is the single most-quoted teacher prediction of the twentieth century, and it is straightforwardly false as stated. GSMA figures put smartphone adoption near 70 percent of the global population, and free apps like Photomath will not only solve an equation photographed off a page but show the working.

The argument underneath it survived better than the sentence did. Fluency with number matters: you need to sense that an answer is off by a factor of ten, to do arithmetic while a conversation is moving, and to understand what an operation means before delegating it. Cognitive load research supports automaticity in basic facts, because a working memory busy computing 7 times 8 has nothing left for the actual problem. Every teacher who said the sentence meant this.

So this belongs under "disproved" for the claim and "still true" for the intent, which is exactly the distinction this site exists for. The prediction was wrong. The reason to learn arithmetic was never really the prediction.