A report of a year-long study in which the author engaged in 3D printing activity in order to determine how to facilitate and support skill building, concept attainment, and increased confidence with its use among teachers. Use of 3D printing tools and their applications in instructional settings are discussed. A hierarchy of 3D printing activities of increasing complexity, consisting of print trials, design experiments, and engineering tests, is identified and described. An iterative model that includes the development and refinement of 3D printing tools, geared specifically toward engineering settings is also described.