The unit Measurement Unit Conversions contains lessons and exercises suitable for grades 5-7.
First, we study how the basic concept of decimal numbers can help us convert measuring units. For example, since 0.01 means one-hundredth, then 0.01 m means one-hundredth of a meter -- which is the definition of a centimeter. Then we round and estimate quantities given in various measurement units, and find the error of estimation.
After that, we focus on the metric system and conversions between the metric units of measurement. I have tried to emphasize sensible and intuitive methods for converting measuring units within the metric system, instead of relying on mechanical formulas.
Next, we practice conversions between units in the customary system, using the basic conversion factors and multiplication and division. Then from there we advance to conversions between customary and metric measuring units.
Later, students learn how rates can be used to convert measurement units. This method is in addition to the methods for converting measurement units that were explained earlier in the unit. It does not mean that students should “change over” and forget what they learned earlier—it is simply a different method for doing the conversions. Some students may choose one method over another; some may be able to master all of the methods. Most will probably choose one method they prefer for doing these conversions.
Next, the lesson on maps gives a different real-world context for measurement units and conversions between them, since calculating the real distances from map distances or vice versa involves both using a scale ratio and conversion of the measurement unit used.
Lastly, the lesson Significant Digits deals with the concept of the accuracy of a measurement and how it limits the accuracy of the solution. Significant digits is not a standard topic for middle school, yet the concept in it is quite important, especially in science. You can consider this topic as optional or reserve it for advanced students.