Current research has not fully explored how summer programming camps can help students increase motivation and interest to pursue computing career, and their programming knowledge. Informal CS education through summer programming camps provides K-12 students the opportunity to learn how to code through fun and interactive activities outside of their typical classroom experiences. In this study, we examined the effectiveness of a weeklong summer programming camp for promoting students' motivation and interest in programming, and their programming knowledge. Participants were 19 middle school students from rural Washington. Students participated in a project-based learning approach through game development in Python. Using a within-subjects design, we analyzed students' pre and post motivation and knowledge assessment scores. Results from the analysis indicated a significant improvement in post-test programming knowledge scores (d = 0.93). The findings also indicated that students were able to achieve basic abstraction and algorithmic thinking but not code analysis and debugging skills. On their motivation to pursue computing careers, the results did not show any difference before and after the camp due to their prior existing interest in attending the camp.