In this paper, we present a collaborative cross-reality game for two players, Lab2, which blends tangible board game and immersive virtual reality playing spaces in a gameplay that aims to promote and train collaborative behaviour. As collaborative learning has been stressed as an effective teaching method for many years, Lab2 could assist learners in exploring and further developing their collaborative skills in a playful manner. One player controls a physical game board showing a moveable maze of “pathway” tiles, while the second uses a spatially tracked HMD to find himself inside a virtual-reality version of the game-board’s maze. The goal of the game is to collect a set of tokens hidden inside the maze. Reaching these tokens requires the players to collaborate via their complementary roles. We will first outline the game design concept and then detail the user-testing based evaluation of our game prototype.