What does "fair testing" mean in science?

[PeaMcLean]

DS's school report says he needs to develop his understanding of it. he's 7.

What does that mean?

Basically that when you test something you only change one factor, keeping the others the same, thus fair. So if you wanted to test if temperature of water changed how fast sugar dissolved you would change only the temperature of water, keep the containers the same, the amount of water the same, the amount of sugar the same and so on.

Hope that helps..

I see, thank you.

DS told me last week he doesn't do science at school () so there's no point asking him what sort of experiments he's been doing!