NSES Content Standard E 
Science and Technology: Abilities of technological design 
Grades K-4, page 137 

Propose a solution. Students should make proposals to build something or get something to work better; they should be able to describe and communicate their ideas. Students should recognize that designing a solution might have constraints, such as cost, materials, time, space, or safety. 
 

 
Benchmark 3B The Nature of Technology: Design and Systems
Grades K-2, page 49
People may not be able to actually make or do everything that they can design.

Benchmark 3B The Nature of Technology: Design and Systems
Grades 3-5, page 49
There is no perfect design. Designs that are best in one respect (safety or ease of use, for example) may be inferior in other ways (cost or appearance). Usually some features must be sacrificed to get others. How such trade-offs are received depends upon which features are emphasized and which are down-played.

Benchmark 3B The Nature of Technology: Design and Systems
Grades 6-8, page 51
Design usually requires taking constraints into account. Some constraints, such as gravity or the properties of the materials to be used, are unavoidable. Other constraints, including economic, political, social, ethical, and aesthetic ones, limit choices.

Benchmark 3C The Nature of Technology: Issues in Technology
Grades 3-5, page 54
Scientific laws, engineering principles, properties of materials, and construction techniques must be taken into account in designing engineering solutions to problems. Other factors, such as cost, safety, appearance, environmental impact, and at will happen if the solution fails also must be considered.