In this article, we provide novel survey evidence on middle schoolers' knowledge and on how such knowledge evolves in the process of high school track choice. Children in our study display only partial awareness of the set of available tracks, and they report low confidence regarding their beliefs (i.e., substantial belief ambiguity) about their likelihood of a regular high school path. This is especially the case for lower-ranked tracks. Students start 8th grade with greater information about their preferred alternatives and continue to concentrate their search in the months before pre-enrollment. Children from less advantaged families display lower initial perceived knowledge and acquire information at a slower pace, particularly about college-preparatory schools.