"When you teach, you have a lesson plan, but you're not bound to follow it. You play, follow up, improvise and adapt, as the situation dictates. It's intellectual engagement, and you want to be engaging. So having a real, live audience makes a difference."

Bresler said that the commitment to a third-party audience helps the teacher "see, perceive and make sense of what they're trying to communicate on a very different level."

Tests involving children as young as three months suggest biological differences and not social pressures dictate which toys children like to play with.

The U.S. study looked at babies aged three to eight months - before they can identify even the gender of other people.

Researchers placed a doll and truck inside a puppet-theatre style box and showed them to 30 children - 17 boys and 13 girls - for two ten-second intervals.

The findings, from researchers at Texas A&M University, overturn conventional wisdom that children's toy preferences are down to social conditioning.