A video by Khan Academy going over indirect measurement. Start at 6:20 if you want to skip the example scale diagram problem.
Grades 6 through 7 Material from CK-12Preview Assign
See when students have begun their work. Or not.
Use ratio and rate reasoning to solve real?world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations.
Solve problems involving scale drawings of geometric figures, such as computing actual lengths and areas from a scale drawing and reproducing a scale drawing at a different scale.