I noticed an interesting short paper on "Exposing Undergraduate Students to Database System Internals". Written by Joe Hellerstein at UC Berkeley and Anastasia Ailamaki at CMU, it describes their experience using PostgreSQL to teach courses that introduce undergraduate students to DBMS internals. This provides some context for the student projects on hash-based aggregation and other topics that have been occasionally mentioned on -hackers in the past (e.g. here).