Research has shown that undergraduates have problems understanding astronomical concepts, especially size, scale, and structure. One way to evaluate understanding is to use concept inventories. Therefore, the purpose of this study was to begin the development of the Size, Scale, and Structure Concept Inventory (S3CI) to assess understanding of these concepts in introductory undergraduate astronomy courses for majors and non-majors. A secondary purpose was to determine the impact of a newly developed WorldWide Telescope (WWT) enhanced lab on parallax, part of a suite of WWT enriched labs for introductory astronomy courses currently under development. We present in this paper preliminary results from the first WWT-enhanced lab on parallax. In Fall 2013, a beta version of the S3CI was piloted in an introductory astronomy course at a small private university. An item analysis was done and estimates of internal consistency reliability were determined using the Kuder-Richardson Formula #20 (KR20). The impact of the newly developed lab was also evaluated using a sub-test of six questions from the S3CI.