There are two kinds wheels,one kind with total two wheels,can't climb the stairs,it is flashing wheels,the number 1,2,3,4,9,11,13,15,17,19 are two wheels style,

the other kind with six wheels,can climb the stairs,not flashing wheels,the number 5,6,7,8,10,12,14,16,18,20,21,22,23,24,25,26 and 27 are six wheels style.

When you order,please kindly pay attention to it.

Number 1-20 normally suit for grade 2-6
Number 21-27 normally suit for grade 1-2