When teaching my third grade students about linear measurement, one of the hardest concepts for kids to grasp is the difference between yars, feet, and inches.
We do a FUN project where the kids actually measure the football field.
First, I send out an email to all of the teachers in the school and ask them to borrow as many yard sticks as possible. (We need 100 of them.)
Then we lay them out, end-to-end on the school's football field. They then have a clear understanding of how long a yard is. And how many yards it takes to cover a whole football field.
Also, we take individual rulers and measure between the yard lines so kids can see that 3 feet makes one yard.
When we collect our yardsticks and go back to the classroom, the kids must then calculate how many rulers it would have taken to cover the 100 yards of the football field. They also calculate how many inches long a football field is.
It's a great lesson because it helps them to visualize the concepts in a way they'll always remember.