What algebraic expressions mean

This is a good resource for pupils beginning in algebra, especially those who like to know exactly what's going on and why. The left hand column of the resource gives written examples showing that, for example, 3 x a x a can be written as 3a(squared). It proves this by working the same example through with numbers. 3 x 4 x 4 = 3 x 4(squared) = 48.
The right hand column requires the pupil to have a go at writing a simplified algebraic expression based on the pattern in the left column. There is room to do a 'numbers version' if that helps.
At the bottom, there is a challenge to work the idea backwards, expanding expressions such as 6fg to find out what's really going on inside that expression.