This qualitative study investigates the extent to which urban middle-school science teachers' beliefs about their students' astronomy learner characteristics were influenced by their partnership with an astronomer in their classroom. Twelve urban middle-school science teachers were interviewed after their participation in Project ASTRO during the 2009-2010 academic year using semistructured, in-depth interview techniques. Constant comparative analysis was used to analyze the interview transcripts. Themes that emerged from the data were formulated in relation to the study's grand tour research question. The findings suggest that teachers believed that their partnership with an astronomer largely influenced their students' level of motivation and increased their students' level of questioning. Teachers also believed that their astronomer partner positively enhanced their students' learning experiences in astronomy by making the subject area more realistic, relevant, and scientifically rigorous. Additionally, the study showed that teachers believed that their partnership with an astronomer in their classroom positively affected their students' behaviors and attitudes in middle-achieving and high-achieving schools. The study further revealed that partnering with an astronomer had a relatively minor impact on urban middle-school science teachers' beliefs about their students' mathematical cognitive ability. The implications of these findings suggest that astronomer-educator partnerships may enhance urban middle-school students' learning experiences in astronomy and promote their engagement with science. However, new educational approaches need to be developed and assessed to help bolster students' understanding of astronomy, especially in low-achieving urban school settings. (Contains 2 tables and 1 note.)