In 5th grade we had a great conversation about exponents and powers of 10. Some students have older siblings who introduced the concept to them but most had never heard of them before. It really helped them connect the idea of place value and that the digit to the left is 10 x the digit to the right.
In 6th grade we tackled word problems involving fraction and decimal division/multiplication. We did this similar to the ratio word problems and it had almost better results! Since we use Math in Focus, the problems almost require using the bar model. Some you don't need it but others it just makes the problem so much easier at their level.
For example this fun problem: Mike had a large tropical fish collection. He gives 2/3 of his fish to a local high school. Then he gives 2/5 of the remaining fish to an elementary school. In the end, he has 30 fish left. How many fish did Mike have at first.
Three of my 5 groups got it using the beautiful bar model! Best of all,the rest saw how much easier the bar model made it look.