Model-eliciting activities (MEA), specially designed client-drive, open-ended problems, have been implemented in a first-year engineering course and in secondary schools. The educational goals and settings are different, but the design of an MEA enables it to be versatile. This paper will introduce the reader to the principles that guide MEA design and demonstrate the flexibility of implementation by describing the use of an MEA, Aluminum Crystal Size, in these two educational settings. [For "Quantifying Aluminum Crystal Size Part 2: The Model-Development Sequence," see EJ1063797.]