Ubiquitous computing, as a subfield of computer science, has traditionally been associated with a set of principles expressed (loosely but tellingly) with terms like transparency, invisibility, and the like: essentially, the idea is that people should be able to use ubiquitous computing artifacts while hardly being conscious that they are doing so. We argue that, as a design principle, "invisibility" has advantages in some domains; but that it has powerful, and ultimately counterproductive, connotations for educational design. We present an alternative set of potential design principles for educational ubiquitous computing, stressing values such as expressiveness, creative control, and aesthetics; and we illustrate these principles with several projects undertaken in our lab. Keywords Ubiquitous computing and education; transparency; educational technology.