Last summer I taught a class on introduction to programming to high school students through the LEAD Program. This was the inaugural LEAD Computer Science Institute at UC Berkeley. The program aims to get promising minority high school students (rising 10th and 11th graders) interested in computer science through an intense, focussed 3 week program. The students came from all over the country and stayed on the UC Berkeley dorms.
Microsoft recently started a program in Seattle where they send Engineers to teach classes to High School students with the intent of encouraging them to consider studies in Computer Science. The article cited that the kids really enjoyed their trips to visit Microsoft's campus.
For students in the Seattle area, Microsoft tries to drum up excitement in technology by organizing field trips to its campus and discussing the lucrative careers that await them. The students from Rainier Beach High who visited Microsoft last year were buzzing about their trips for days afterward.
I found a similar effect in the class I taught. The LEAD program was backed by Google and Twitter, and after we visited the Google Mountain View campus the kids were extremely excited. The next day in class students were more attentive and excited about the lessons. The visit to an exciting, diverse workplace like Google inspired nearly all of them to seriously consider computer science as a potential career. On their Google campus visit they got to meet Google engineers, ask questions, eat lunch in with Googlers and tour the many amazing items at the Mountain View campus (they were not allowed to ride the google bikes or try the google slide).
If all high-performing high school juniors got a field trip to visit an exciting tech campus just once, it seems like the number of students interested in computer science would likely increase.