Learning to play tennis as a child, I was told by my parents that the best way to improve was to test myself against opponents much stronger than me. I wasn't enthused by this guidance as it meant - at least in the initial weeks - that I was likely to be soundly thrashed.
Today, such a mixing of abilities in class, and indeed in any learning or competitive environment, is widely recognised as one of the most successful ways of stretching and challenging pupils. As long as you impart a "can do" message, rather than reinforce a pupil's negative thinking about their abilities, healthy competition becomes aspirational and ultimately rewarding.
Teachers have various tactics for achieving this: eliciting from pupils - or child-centred learning - is one of the favoured approaches. But even within this format there is considerable scope for a range of clever tactics. One way to boost confidence is by encouraging pupils to explain the topic under discussion to you using statements such as "I don't understand" or "What does that mean?" Everyone loves to know something that somebody else doesn't. Another approach might be to encourage your pupils to explain something complex to you, once they have understood the concept themselves, in easily digested language - a staple of tabloid journalism.
But challenging pupils isn't all about leaving them to find their own path of self-discovery. It also depends on the concepts and questions you set within the lesson - and your readiness to change tack rapidly, which will surprise and stretch pupils further.
Aside from the tennis guidance my parents gave me, one of the most important lessons I learned in my youth came from a secondary school teacher after I received poor exam results in geography (never a strong suit).
Instead of shrugging and agreeing with me that I just wasn't good at placing locations on the world map, she told me there would always be people who were more gifted than me in some areas. But she gently explained that this wasn't a reason to give up. She was right. And it's a lesson you can apply to all areas of life.
Jo Knowsley is acting editor of TESpro, firstname.lastname@example.org @tes.