Rather than teach children to use key words to solve math problems (an inherently unreliable method), we need to teach them the SCHEMA of such problems. That is, what is the underlying structure and logic of a word problem? Think of a graphic organizer that children use in learning story structure (characters, setting, problem, solution, etc.) and transfer that idea to a math word problem. We can compare quantities, find totals or differences, examine the change that takes place... Here are some website with further information.
There's an IRIS module with a long page about using schema-based instruction in math: