Question: I'm currently playing a piece which requires big stretches of large intervals across the keyboard. It slightly hurts when I do so, and I am wondering if I should continue to practise like this.

[![Bartok Suite op14 - Allegretto](https://i.stack.imgur.com/6cfvl.png)](https://i.stack.imgur.com/6cfvl.png)

My piano teacher suggests fingerings with a combination of 3 1 and 2 1 in the L.H.

Answer: 
Don't persist in doing anything that hurts. 

As commented, if you show us the passage in question we might be able to suggest a strategy.
Sadly, some piano music simply can't be played as written with small hands without some modification. If you're trying to play certain pieces by, say, Liszt or Rachmaninoff (two famously large-handed performers - seriously, they still make plaster casts of their hands so you can compare to an average human - they're enormous), you may not be able do as wide a spread as they could, and so some music they wrote may be physically beyond your capability. There are exercises you can do to increase your hand span, but they can only take you so far. You may find you need to roll chords rather than play all the notes at once, or even omit or transpose some notes if your hands cannot reach them all. Many publishers include suggested variations for small hands on some difficult passages.