Interactive tabletops are an exiting new platform for supporting children's collaboration. With design guidelines and standardized interaction principles still immature, there is a considerable need for iterative prototyping to define the task and interface. Lo-fi prototypes-using cardboard, paper, etc.-are easy to develop, flexible to adjust during design sessions, and intuitive for users to manipulate. Using them can be a valuable step in designing tabletop applications. In this paper, we detail the design process of two tabletop applications, concentrating on the role of lo-fi prototyping. TransTime is a pattern game for 5-6 year olds to engage how time progresses. OurSpace is a design tool for 7-9 year olds to arrange desks and assign seats for students in their classroom. By comparing the experiences, we arrive at a better understanding of the benefits, challenges, and limits of using lo-fi prototypes to design interactive-tabletop applications for children. Categories and Subject Descriptors H.5.2 [Information Interfaces and Presentation]: User Interfaces -user-centered design. Design, Human Factors. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.  Interactive tabletops, co-located collaboration, lo-fi prototyping Interactive tabletops are large horizontal displays that several users can interact with simultaneously. Depending on the underlying technology, users interact through direct touch [3, 7] , pen input, or by moving trackable objects [10] . As single display groupware [29] , they lend themselves to colocated collaboration. Several projects have used these with children to promote creativity [2, 12, 13] , interaction [19] , and learning in a variety of subject domains: reading [28], fractions [24] , and the physics of light [20] . While there is growing interest, little has been written about design methods for developing interactive-tabletop applications for children. In this paper, we examine one design method, lo-fi prototyping, and demonstrate its usefulness as part of a usercentered design (UCD) process. We detail the role of lo-fi prototyping in the development of TransTime and OurSpace. We share our experience to concretely demonstrate the value of this approach. We then synthesize across these designs and related literature to examine the benefits, challenges, and limits of this approach. Our aim is to provide a useful guide to others interested in designing interactive-tabletop applications for children. Creating software that users find useful and usable is challenging. Although seductive to novice programmers, programming software to specifications is not effective. User feedback is required to form an accurate impression of how people will appropriate a technology [18] ; this requires iterative development. To ensure that development time is not wasted on implementing flawed ideas, users should be involved early in the design process [17] . Since it is often not 138
Rick et al. performed a study of low-fi prototyping of tabletop applications for children and concluded that low-fi prototyping is a useful approach, although they recommend adapting desktop applications to digital surfaces REF .
Lo-fi prototyping to design interactive-tabletop applications for children
IDC
Engineering Computer Science