ok i had the ultimate test- b/g twins

DD would fall right off a piece of play equipment, do a elegant roll and land on her feet without even a crinkle on her clothes
DS - SPLAT!
boys more clumiers- why? more distracted/ cant do more than one thing at a time and easily lose concentration on what they were doing at the time
BTW i always found that all kids become clumsy during a growth spurt. The muscles that grow have to learn to co-ordinate and do things that they have never learnt before- that is why kids always go backwards when they are learning something like swimming lessons during a growth spurt!!!
boys also tend to be better a different motor skills to girls at this age- DS got off training wheels quicker than DD, where as DD learnt to whistle, click her fingers and tie shoe laces quicker than DS

there is definately a difference between boys and girls !!