ToyDBMS -- a toolkit for teaching a DBMS development course. It consists of a set of problems, a reference implementation, and a testing system. The idea is to hand out a skeleton of a query engine which students gradually enhance throughout the semester. This way, at the end of the semester they obtain a system capable of processing moderately interesting queries. During the semester students implement such DBMS components as: query rewriter, a set of relational operators, a statistics module, and a simple rule-based query optimizer. The system is used during the “DBMS design” course in the Higher School of Economics (Saint-Petersburg, Russia), and the ITMO University (Saint-Petersburg, Russia). The aim of this project is to design new problems and improve the feature set of the testing system.