Maybe it is the name that is difficult, but there are some children that have difficulty understanding expanded form. A large visual with each number separated into a different color box can be very useful in helping students to separate each individual number for expanded form. This solidifies the concept that a 4 in the hundreds place is really worth 400. Large visuals are also very useful in a situation like this where it would be very difficult to count 400 pieces of an object out. Place value blocks that actually include a 100 cube are a great idea if a teacher needs hands on.